Despite its inhospitable appearance and lack of any ... - Udine Cultura

Fauna 

FABIO STOCH 

Despite its inhospitable appearance and 

lack of any sign of life at first sight, 

groundwater is populated by large 

numbers of animal species of various 

taxa. These animals are generally very 

small, even tiny (between three-tenths 

of a millimetre to one centimetre). Only a 

few exceed one centimetre, and even 

fewer are quite big, like the underground 

prawns of the genus Typhlocaris or the 

olm (Proteus anguinus). 

Larva of stygoxene chironomid 

● Stygoxenes. Not all organisms found in groundwater are exclusive to it: in 

fact, many of them are typical of surface environments and, through either 

active or passive dispersion, accidentally penetrate underground. They are 

therefore occasional guests in this habitat, to which they are generally carried 

by water percolating from the surface. This situation is very frequent in surface 

and underground karstic aquifers, with infiltration passages which are very 

efficient (sinkholes) or slower (like micro- and macro-fissures in limestone). 

The accidental guests occurring in groundwater are called stygoxenes. They 

do not have adaptations enabling them to survive in the harsh underground 

environment, where food supply is more restricted than in their habitat of 

origin. However, in particular conditions - for example if the aquifer is 

organically polluted - stygoxenes find optimal conditions for their survival and 

may even reproduce in hypogean (underground) habitats. Their populations 

may be quite large and compete with local ones, to the point of replacing them 

completely. They may also play important roles as prey or predators of 

underground species. 

● Stygophiles. Stygophiles are organisms that exhibit some adaptation to life 

in groundwater environments, and may reproduce in both surface and 

underground waters. Stygophiles live within surface water-groundwater 

interfaces like springs, humid soil, wood litter and moss. These habitats share 

several characteristics with the underground environment, in particular 

darkness and limited living space. This is why stygophiles often have pre- 

Monolistra schottlaenderi (top) and Monolistra racovitzai (crustacean isopods, 7x) 

41

42 

adaptive features to life underground, which enable them to survive in 

transitional environments: they are often partially or totally depigmented and 

have reduced or totally absent visual organs. From the evolutionary viewpoint, 

since groundwater is a secondary colonisation environment, the species now 

found exclusively here are thought to have been stygophiles in the past. But 

the contrary cannot be ruled out - i.e., that all past stygophiles are now 

exclusive groundwater dwellers. Evolutionary destiny depends on the 

opportunities which single stygophilic species had of colonising groundwater, 

surviving and successfully reproducing. 

Stygophiles which regularly frequent the subterranean environment where they 

can reproduce, but which do not have marked adaptive characteristics, are 

called substygophiles. They include, for instance, some aquatic benthic insects 

found in watercourses, where they may spend the early phases of their 

development in the fluvial hyporheic environment. This is a winning adaptive 

strategy as regards avoiding predators, but their life-cycle is always completed 

in shallow waters, and adults often inhabit the subaerial habitat. This is true of 

many ephemeropterans, plecopterans and dipterans, mainly chironomids. 

Conversely, those stygophiles which show not only marked pre-adaptations 

but also an elective preference for the subterranean environment, where they 

are regular guests, are called eustygophiles. This is the case of many molluscs 

and crustaceans. 

Paracyclops imminutus (stygophyle) 

● Stygobionts. Animal species closely associated with underground 

environments, on which they depend for completing their life-cycle, are called 

stygobionts. They often have marked adaptations to underground life like 

depigmentation, anophthalmy (absence of eyes), well-developed sensory 

organs, and a reduced fecundity rate (described in the chapter on the 

ecological aspects of groundwater). These adaptations are partially shared by 

terrestrial troglobionts (cave-dwelling species) and by those living in soil 

(endogean species). Stygobionts may be ubiquitous and live in all types of 

aquifers, and sometimes in marginal waters (for instance, under dead leaves in 

humid forests), or they may be associated with specific habitats, like 

phreatobionts, which live exclusively in saturated alluvial aquifers, and karstic 

stygobionts, which are limited to aquifers in limestone and evaporites. 

A clear distinction between these ecological categories is difficult to make, 

and there are many intermediate levels. In some taxa, of which all species 

appear to be pre-adapted to life in humid soil and groundwater, like 

nematodes and some families of oligochaetes, it is impossible to divide them 

according to morphology, and their preference for underground habitats is 

evident from the frequency with which they are found there. 

This chapter on groundwater fauna describes exclusive dwellers, i.e., 

stygobionts. We will discover a fascinating multitude of dark-loving organisms, 

with sometimes bizarre morphological adaptations. 

Niphargus steueri (stygobiont) 

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44 45 

Methods for sampling and analysing groundwater fauna 

Fabio Stoch 

Groundwater habitats are difficult to 

reach, and researchers have had to 

come up with ingenious methods for 

sampling and analysing underground 

fauna which, according to the depth and 

accessibility of aquifers, are sometimes 

expensive and so complex that only 

specialised research institutes can carry 

them out. 

In karstic waters, traditional sampling 

methods include: 

● continuous filtering of trickling water 

funnelled into containers with filters 

which are periodically emptied; 

● collection of percolating water in 

gours and micro-gours, by means of 

rubber pumps or syringes; 

filtering of concretion water with 

plankton nets (60-100-µm mesh) which 

are emptied with rubber piping; 

● direct filtering of water from large 

pools with plankton nets with handles; 

● in streams and small watercourses: 

after coarse debris has been shaken out, 

water is filtered through plankton nets 

(with semi-circular openings 20-25 cm in 

diameter); 

● direct collection of large organisms 

with aquarium nets and tweezers; 

● in order to collect large predatory 

crustaceans (1), traps containing meat or 

tid-bits of food can be placed in suitable 

positions in open cans (to avoid the 

death of animals trapped inside, if the 

trap itself is lost); 

● placing artificial substrates (twisted 

nylon netting compressed in tubes, or 

tubes filled with locally collected washed 

sediment) which are periodically emptied 

in order to analyse the colonisation of 

various types of substrates. 

Collecting specimens from wells or 

boreholes in alluvial soils may be carried 

out with: 

● modified plankton nets (Cvetkov nets) 

with valves to prevent material from 

escaping when the nets are quickly lifted 

and replaced on the bottom of the well 

to agitate the sediments (2); 

● various types of pumps (peristaltic, 

rotor, compressed-air), according to 

water-table depth (rotor pumps of 

greater power unfortunately easily 

destroy material). 

Lastly, in flooding watercourses where 

collection is concentrated in upwelling or 

outwelling stretches (see chapter on 

ecology), two methods are used: 

● Karaman-Chappuis method: a hole is 

dug along the shore of a watercourse, 

and the water permeating from nearby 

sediments is collected and filtered 

through a plankton net; 

● Bou-Rouch method: a hand-pump (3) 

is used to remove interstitial water from 

the bed of a watercourse, by means of a 

Filtering trickling water with a plankton net Equipment for sample collection 

1 

2 

perforated tube inserted deeply into the 

sediments (for a detailed description of 

this method, see Teaching Suggestions). 

Research teams with the most recent 

equipment can use drills to place 

piezometers at varying depths, from 

which groundwater is extracted with 

pumps and filtered through plankton 

nets. 

Other, quite expensive methods, like 

freeze-coring, use liquid nitrogen to 

freeze sediment cores collected from 

boreholes and subsequently examined 

in the laboratory. 

More advanced research methods 

involve inserting transparent perspex 

piezometers with optical-fibre videocameras 

into the soil or sediment in the 

river bed. In this way, researchers can 

analyse large organisms in their natural 

environment without disturbing the 

underground community. 

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46 

■ Poriferans 

Among all stygobionts, sponges are certainly the least frequent and most 

primitive. These essentially marine organisms (there are few freshwater 

species belonging to the spongillid family) frequently colonise coastal caves 

shrouded in partial darkness. There is, however, at least one exception to this 

rule: Higginsia ciccaresei, a sponge which has recently been collected by 

scuba divers exploring the Zinzulusa Grotto in the Salento (Apulia). The 

species is endemic to the cave, and was found at a distance of 250 m from its 

entrance, at a depth of 12 m, in total darkness. The morphological 

characteristics of this species, like its depigmentation, have led researchers to 

consider it a stygobiont. 

■ Platyhelminthes 

Flatworms are a primitive phylum of 

free-living or parasitic organisms. 

Stygobiont planarian worms are 

Atrioplanaria morisii 

generally depigmented, eyeless, with 

slow reproductive cycles and high 

numbers of chromosomes. 

In Italy, although very little is known 

about these organisms living in 

phreatic environments, which are 

certainly inhabited by many minute 

creatures (micro-turbellarians), some 

species living in karstic waters are well 

documented. Dendrocoelum collinii lives in pre-Alpine caves and in France, 

and D. italicum in Lombard caves, although the taxonomic position of Italian 

populations of both species requires revision. The genus Atrioplanaria is found 

in caves in Sardinia, central-southern Italy (A. racovitzai) and southern 

Piedmont (A. morisii); Polycelis benazzii lives in Ligurian caves. The taxonomy 

of these genera is uncertain, due to the fact that it requires examination of 

living specimens and the use of complex histological and karyological 

methods. This is why these animals are seldom included in lists of fauna. 

However, being predators, their trophic role in underground ecosystems may 

be of local importance. 

The taxon of temnocephalid flatworms is of uncertain position. These 

ectoparasitic species sometimes abound on the gills of crustaceans like 

stygobiont amphipods and decapods, whose haemolymph they suck. Very 

small (2 mm maximum), these animals have tentacles and adhesive discs with 

which they attach themselves to their hosts. In Italy, only three genera have 

been found so far (Bubalocerus, Scutariella, Troglocaridicola); they are 

parasitic on stygobiont shrimps of the genus Troglocaris which live in 

saturated karstic waters in the Karst areas of Trieste and Gorizia. 

■ Molluscs 

All Italian stygobiont molluscs belong 

to the gastropod class, in particular to 

the hydrobioidean superfamily (spring 

snails). Although they are common in 

Italian groundwater, with about 70 

species described, and are found in all 

types of habitats - except for the 

vadose zone of karstic aquifers - spring 

snails are still little known from the 

taxonomic viewpoint. This is because 

many species are only known by their Hadziella ephippiostoma 

shells, which are found in springs and 

hyporheic water, suggesting that the elective habitat of these populations is the 

deep, almost inaccessible underground environment. Many empty shells are 

found in river sediments, and therefore their unknown underground habitat 

may in fact be very far from where they were actually found. This is why their 

genera and species described in the past need to be revised. 

The shells of spring snails have various shapes. They are generally towershaped, 

conical and cylindrical, often truncated. Some genera have disc- and 

spiral-shaped shells. Stygobiont species of spring snails are usually very small 

(for example, the adults of the genus Hauffenia have a diameter of 2 mm and 

are only 0.7 mm high). The opening of the shell is generally large and round, 

closed with a thin, horny, egg-shaped lid, the operculum, which protects the 

soft tissues of these animals. They move by means of a complex set of 

muscles, the foot, which flattens ventrally and adheres to the substrate 

allowing the snails to crawl. Stygobiont spring snails feed on micro-particles of 

organic matter, encrusting micro-organisms and bacterial biofilms, which are 

scraped and ground by their radula, an organ bearing several rows of minute 

teeth. Except for a few species living in brackish water, most Italian spring 

snails live in freshwater and are crenobionts (spring-loving) or stygobionts. 

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48 

Shells of gastropods Iglica vobarnensis, Paladilhiopsis virei and Hauffenia subpiscinalis (from top to 

bottom, ca. 30x) 

Crenobiont species (genera Bythinella and Graziana) may enter groundwater 

bodies and burrow into interstices, probably in search of food, and therefore 

behave as stygophiles. A large number of endemic species of the genera 

Bythiospeum, Iglica, Istriana, Hadziella, Paladilhiopsis and Phreatica are 

strictly stygobiont, and live deep within karstic and alluvial underground 

networks in northern Italy. Some species, living in Alpine-Dinaric areas, are 

exclusive to the eastern Pre-Alps and are often strict endemics (like 

Paladilhiopsis robiciana, Phreatica bolei, Hauffenia tellinii and Belgrandia 

stochi). The area with the fewest species is the Piedmont Alps, with some 

endemic species of the genera Alzoniella, Iglica and Pseudavenionia. The 

Apennines host a small number of local endemics of the genera Pezzolia, 

Alzoniella, Pauluccinella, Orientalina, Fissuria and Islamia. Exclusive inhabitants 

of Sardinia are the genera Sardhoratia and Sardopaladilhia. Sicily hosts only 

one crenobiont species, Islamia cianensis. Thermal waters contain particular 

species of Bythinella and Belgrandia. 

■ Polychaetes 

Polychaete worms are generally sea animals, and only a few species colonise 

anchialine coastal waters (land-locked bodies of water with a subterranean 

connection to the sea), and even fewer species are adapted to underground 

freshwater. Among them are two stygobiont species of great biogeographical 

interest. 

The nerillid Troglochaetus beranecki is an ancient thalassoid species (that is, 

one with marine affinities) originating from members of psammon in Tertiary 

epicontinental seas, from which it invaded underground freshwater. The 

characteristic of this species is its vast distribution area. In Europe, 

Troglochaetus beranecki is found in large rivers (Rhone, Garonne, Rhine, 

Weser, Danube, Oder, Elbe), in Finland and in Alpine streams. It has also 

been found in interstices in river beds of Colorado and Montana (up to 3050 

m), although further molecular analyses are required to establish whether all 

these populations are really conspecific. Fewer numbers are found in caves 

of Switzerland, Germany, Poland, Hungary and Romania. In Italy, the species 

has recently been found in interstitial environments (Trentino) and in caves 

(Lessini Hills and Carnic Pre-Alps). This distribution is very wide, and 

includes ice-covered areas where underground fauna is minimal if not totally 

absent, and the rare stygobiont organisms have a remarkable capacity for 

adaptation, which enabled them to colonise these areas in post-glacial 

periods. 

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50 

Alkaline waters in karstic caves in Gorizia and Trieste host the second Italian 

stygobiont polichaete, Marifugia cavatica. It belongs to the serpulids, which 

are marine polychaete worms living in limestone tubules. Marifugia cavatica, 

probably a micro-filterer, forms dense colonies that occasionally carpet 

extensive areas of walls of underground streams with tubules up to 1 cm 

long. The Marifugia formation is a little-known microhabitat rich in microfauna 

(protozoans, gastropods, oligochaetes, copepods, isopods and 

amphipods) that populates, like the colonies of marine serpulids, the complex 

mosaic of spaces between tubules. The species lives in the Dinaric region as 

far as Albania, together with other species of ancient marine origin, like 

isopods of the genus Sphaeromides and amphipods of the genus Hadzia, of 

probable Tertiary origin. 

■ Oligochaetes 

Oligochaetes are freshwater and marine terrestrial annelids whose bodies are 

made up of segments (metameres) without appendages, with rows of 

transversal, movable bristles (setae). The shape and distribution of the setae 

play an important role in the taxonomy of this group. Earthworms are usually 

detrivorous and microphagous, and colonise microhabitats rich in organic 

matter. In Italian groundwater, the most common are the lumbriculid and 

Troglochaetus beranecki (ca.50x) Cernosvitoviella sp. (ca. 40x) 

tubificid families, together with the aquatic and semi-aquatic species of 

enchytraeids. 

The identity and similarity of groundwater oligochaetes have only recently been 

partially established, and research is beginning. The main problem in defining 

an oligochaete as stygobiont lies in the fact that many surface species (living in 

sediments of surface water and sometimes in humid soil) are pre-adapted to 

life in hypogean habitats (they are depigmented and anophthalmic). It is 

common practice to define as stygobiont those species which, as far as is 

known today, have exclusively been found in groundwater. 

The parvidrilid family is certainly the most interesting among the taxa recently 

found in Italy, from the Pre-Alps to Sardinia. So far, all records have been ascribed 

to the same species, Parvidrilus spelaeus. They are exclusive inhabitants of 

vadose zones in Italian caves, where they colonise the silty, muddy sediments on 

the bottom of concretions, pools of trickling water and interstices of hypogean 

streams. Presumably, the family has an ancient marine origin. 

Among the numerous species of tubificids found in Italian groundwater, there 

are the genera Haber (H. monfalconensis in springs of the Julian Pre-Alps and 

Trieste Karst, and H. zavreli in groundwater in Umbria and Emilia Romagna), 

two endemics of the genus Rhyacodrilus, recently described (R. gasparoi in 

Pre-Alpine caves and R. dolcei in small concretions of the Trieste Karst), 

Tubifex pescei, in phreatic waters of Umbria and Marches, Abyssidrilus cuspis, 

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52 

collected in phreatic waters in Umbria and caves of Liguria and Friuli Venezia 

Giulia, Sketodrilus flabellisetosus in the Trieste Karst, and Aktedrilus ruffoi, 

recently described on specimens found in interstitial environments of the river 

Tione (Verona). 

Enchytraeids are less well-known, and several species of Cernosvitoviella, found 

in Pre-Alpine caves and considered to be stygobionts, are still being examined. 

■ Ostracods 

Ostracods (from the Greek ostrakon, shell) are a diversified group of small 

crustaceans, whose body is enclosed by a bivalve carapace made of calcite, 

their unmistakable characteristic. Their carapace may be egg-, bean- or 

trapezoid-shaped, and is often knobbly or dimpled. The number and shape of 

their appendages is generally the same. 

Freshwater species have eight pairs of appendages, four of which are 

cephalic (antennules, antennae, mandibles, and maxillulae), three thoracic, 

and one caudal (uropod). They are generally small-sized (stygobionts 

seldom exceed 1 mm in length), and are found in all types of surface- and 

groundwater. 

Despite their large numbers in groundwater, both in caves and alluvial 

aquifers, stygobiont mussel shrimps are little known in Italy, and many 

Cypria cavernae (ca. 100x) Pseudolimnocythere sp. aff. hypogea (ca. 100x) 

species are still being studied. Among the most interesting is Cypria 

cavernae, thought to be endemic to alkaline karstic waters in Gorizia, Trieste 

and Slovenia. Other species are associated with anchialine habitats, like 

those in underground lakes of coastal caves in the Salento in Apulia 

(Trapezicandona stammeri, Pseudolimnocythere hypogea). Specimens of 

the genus Pseudolimnocythere were found in the brackish water of the 

Poiano springs, which issue from Triassic evaporites in the upper Val 

Secchia. 

A very interesting genus from the palaeogeographical viewpoint is 

Sphaeromicola. It is a commensal species living exclusively on stygobiont 

isopod crustaceans of the genera Monolistra (Sphaeromicola stammeri, in the 

Pre-Alps) and Sphaeromides (Sphaeromicola sphaeromidicola, in the Isonzo 

Karst). The same genus includes a commensal species on marine amphipod 

crustaceans, showing how both these ostracods and their hosts had marine 

ancestors. 

Mussel shrimps are very interesting in palaeogeographical research, because 

their shells are easily conserved in sediments, where they fossilise. The large 

numbers of fossil species, together with the great diversity of living ones, 

provide detailed information about the evolution of the animals of this class. 

Unfortunately, since stygobiont species are little known, have rarely been 

used to analyse the origin and evolution of stygobiont fauna. 

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■ Copepods 

Copepods form the largest and most diversified group of crustaceans, with 

13,000 species described, half of which are commensal or parasitic on other 

organisms. Copepods are divided into ten orders, four of which include freeliving 

species in groundwater (calanoid, cyclopoid, gelyelloid and harpacticoid 

copepods). Except for gelyelloid copepods, which live in the Jura mountains 

between Switzerland and France, the other three orders are found in Italy. 

Throughout their long evolution, copepods spread across continents, 

successfully colonising any aquatic environment. In freshwater, they live in 

standing waters (from lakes to transient pools), in benthic substrates of streams, 

and in all types of groundwater. They are also found in moss, forest litter soil and 

in wet meadows. Surface copepods spread easily thanks to their resting stages, 

which have been described in previous “Italian Habitats” volumes. These 

stages are also thought to exist in stygobiont species, although there is no 

evidence. This is why species exclusive to groundwater spread with difficulty, 

and are generally endemic. This characteristic is particularly evident in karstic 

systems, whereas species living in alluvial aquifers generally occupy larger 

areas, whose hyporheic habitats may easily be connected. 

Stygobiont copepods are very small (0.2-1 mm) and, with the sole exception 

of calanoids, have one main articulation between thoracic somites 

Speocyclops sp. aff. infernus (ca. 120x) 

(segments) 4 and 5, which divide their 

bodies into two distinct parts, the 

anterior prosome and the posterior 

urosome. The prosome includes the 

cephalothorax and four footed 

somites. The cephalothorax bears six 

pairs of cephalic appendages 

(antennules, antennae, mandibles, 

maxillulae, maxillae and maxillipeds), 

and each thoracic somite has a pair of 

oar-shaped limbs used for swimming 

Antennule of a male harpacticoid copepod 

(ca. 850x) 

(hence the name copepod, from the Greek, meaning “oar-shaped foot”). The 

urosome includes an anterior somite - bearing the fifth pair of thoracic 

appendages - and four appendage-free abdominal somites, the last of which, 

called anal somite, bears the two-branched furca, the unmistakable feature of 

copepods. 

Reproduction requires the participation of both sexes, and parthenogenesis is 

rare. Males are distinguished from females by one (in calanoids) or both (in 

cyclopoids and harpacticoids) antennules modified in the shape of claspers, 

used to hold the female during mating. The fertilised eggs are usually 

contained in one or two egg-sacs carried by the females. Groundwater 

species produce very few eggs, sometimes only one, large. Some stygobiont 

species do not have egg-sacs, and release their fertilised eggs directly on to 

the substrate. Among crustaceans, copepods exhibit the most complete 

metamorphosis. The eggs hatch into larvae called nauplii. There are six 

naupliar stages and, after the fifth moult, the nauplii turn into copepodids, 

which are segmented and similar to adults. Five copepodid stages follow, until 

the sexually mature adult stage is completed. 

Very little is known of the feeding requirements of stygobiont copepods. 

Calanoids, which are part of plankton, are filterers; larger cyclopoids 

(Acanthocyclops, Megacyclops) are predators and feed on other microorganisms. 

Most species are omnivorous, and the main source of food for 

small interstitial copepods (almost all harpacticoids and cyclopoids of the 

genera Speocyclops and Graeteriella) is particle-sized organic matter and its 

associated microbial biofilm. 

● Calanoid copepods. The only Italian stygobiont species, Troglodiaptomus 

sketi, lives in caves in the Karst of Gorizia and Trieste, in Slovenia and Croatia. 

It is commonly planktonic in underground lakes. Very little is known of its 

ecology. 

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56 

● Cyclopoid copepods. So far, only about a hundred species are known to 

live in Italian freshwater, almost all of which belongs to the cyclopids. Few of 

them are planktonic in free waters (some Metacyclops in caves of Venezia 

Giulia, Apulia and Sardinia). Most are epibenthic or interstitial (e.g., genera 

Eucyclops, Acanthocyclops, Diacyclops, Graeteriella, and several 

Metacyclops and Speocyclops). Some species are exclusively associated with 

the vadose zone of karstic habitats, where they inhabit the network of microfissures 

and trickling pools (several species of Speocyclops), and others (such 

as Eucyclops, Acanthocyclops and Metacyclops) are exclusive to karstic 

phreatic waters. Niche segregation is therefore marked, although their habitat 

preferences may vary in different geographical areas. The most common and 

diversified cyclopoids in Italian groundwater belong to the group languidoides 

of the genus Diacyclops: this group of species, many of which are still being 

described, is found in all Italian regions. Other cyclopoid species live in 

restricted areas in the karstic waters of north-eastern Italy (Acanthocyclops 

troglophilus, A. gordani, Metacyclops gasparoi, M. postojnae, Diacyclops 

charon, Speocyclops infernus, to mention only a few), or are widely distributed 

(like Eucyclops graeteri along the Alpine chain, and Acanthocyclops kieferi, 

which colonises Pre-Alpine and Apennine areas). Noteworthy is 

Acanthocyclops agamus, an exceptional endemic species living in caves of 

the Alburni mountains (Salerno) and karstic areas in central Italy. It is an 

interesting example of progenetic paedomorphosis, a phenomenon described 

in the chapter on ecology. From the biogeographical viewpoint, other 

interesting species live in anchialine coastal groundwater, like the cyclopinid 

Muceddina multispinosa, recently described from caves in Sardinia, and 

many species of cyclopids of the genus Halicyclops. All groundwater species 

of cyclopids known so far probably derive from ancestors that used to inhabit 

surface freshwater, and the same applies to species living in brackish water, 

for which anchialine (and marine) environments are secondary habitats. 

Instead, cyclopinids probably have marine origins, although none of these 

species moves far from the coastline. 

● Harpacticoid copepods. Except for species living in coastal marine 

groundwater, which host interesting biocoenoses, six families and 160 species 

of harpacticoids are known to live in continental Italian freshwater, half of which 

belong to the canthocamptids. The order includes numerous benthic and 

interstitial species, commonly found in all types of underground ecosystems. 

Stygobiont harpacticoid species have different origins, and include species 

with recent and ancient marine origin (like ameirids and ectinosomatids), as 

well as those deriving from surface freshwater ancestors, like most 

canthocamptids. There are several endemic species, many of which are limited 

to specific karstic areas (genera Nitocrella, Elaphoidella, Lessinocamptus, 

Moraria, Morariopsis, Paramorariopsis). Several species - only recently 

discovered or currently being described - populate microfissures in limestone 

or the tiny pools formed by trickling and percolating water in the vadose zone of 

caves. The nature of these environments and the isolation of limestone systems 

following karstification have presumably favoured speciation by vicariance, 

producing large numbers of endemics. 

Most endemics in karstic waters are known to live in caves in the Pre-Alps 

and on Sardinia. Recently, species of the genus Pseudectinosoma have been 

found in deep karstic systems of the Gran Sasso Massif, in the Alburni and 

Aurunci mountains. Before this extraordinary discovery, only two species 

were known in this genus, one marine species with amphi-Atlantic 

distribution and the other, stygobiont, known to live in French groundwater. 

The discovery of members of this puzzling genus of ectinosomatids in Italian 

groundwater has great biogeographical importance, as the genus is not 

known to inhabit the Mediterranean area, and Italian freshwater stygobionts 

may be relict species, the only survivors of an ancient fauna which became 

extinct in the marine environment during the salinity crisis that affected the 

Mediterranean in the Miocene. In addition, the surprising discovery of 

Pseudectinosoma galassiae in Australian groundwater confirms the extremely 

Elaphoidella pseudophreatica (ca. 50x) 

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SEM photos of harpacticoid copepods; from top to bottom: Pseudectinosoma reductum, Nitocrella 

pescei and Elaphoidella elaphoides (ca. 200x) 

ancient origin of the genus, which perhaps dates back to a period before the 

onset of continental drift in the Tertiary. 

Groundwater in alluvial aquifers also hosts endemic species like those of the 

genera Nitocrella, Parapseudoleptomesochra and Elaphoidella in much wider 

areas than in karstic environments. A particular feature of the genus 

Parastenocaris is that it fragmented into a myriad of species, most of which 

are known to inhabit only one or a few sites. Italy hosts 35 species - including 

those of the closely related genus Simplicaris - although many more species 

must still be described. Parastenocaris are the tiniest copepods (seldom 

longer than 3/10 of a mm), with worm-shaped bodies and small appendages, 

which enable them to wriggle through the minute fissures between sand and 

gravel grains in interstitial environments. 

■ Bathynellaceans 

Bathynellaceans are an order of totally 

stygobiont syncarid malacostracans of 

extremely ancient origin; some 

researchers believe they diversified as 

long ago as the Palaeozoic in littoral 

coastal waters, lagoons and estuaries, 

from which they colonised continental 

waters before the supercontinent Bathynella skopljensis (ca. 15x) 

Pangaea fragmented, causing them to 

spread into groundwater. Although only hypothetical, this fascinating scenario 

describes bathynellaceans as true living fossils, and shows how research on 

the taxonomy of these stygobionts is closely associated with the great palaeogeographical 

events which modelled the Earth’s surface. 

About 170 species of bathynellaceans are known, all of small size (between 0.5 

and 3.5 mm), anophthalmic and diaphanous, with elongated, sometimes 

worm-like bodies. They do not have shells or brood pouches like isopods, 

amphipods and thermosbaenaceans, and their last abdominal segment (called 

telson) is free; these characteristics clearly identify these malacostracans. 

Italian bathynellaceans are still little known and studied: the first Italian 

representative of this group (Anthrobathynella stammeri) was discovered in 

1954 in the interstitial environment of the river Adige in Verona, and since 

then only a few species have been described, belonging to the genera 

Bathynella, Hexabathynella, Hispanobathynella, Meridiobathynella and 

Sardobathynella. They include exclusively hyporheic interstitial species and 

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those associated with percolating water in caves. They are stenothermal 

animals, sometimes living in cold waters, as they have recently been found 

at high altitudes in the Alps. 

■ Thermosbaenaceans 

Thermosbenaceans, like bathynellaceans, 

are an order of very ancient 

malacostracans, with about 30 

stygobiont species living in fresh and 

slightly brackish water from the 

Caribbean sector to the circum- 

Mediterranean area, eastern Africa, 

Monodella stygicola (ca. 15x) 

Asia, and Australia. This group clearly 

differs from other malacostracans, due 

to the dorsal egg pouch formed by the carapace. 

The evolution of thermosbaenaceans is probably associated with the retreat of 

the sea following uplift caused by plate tectonics. The species often live in 

isolated locations and are of great biogeographical interest. Their name is 

misleading, as it refers to thermal water: in fact, it derives from the first species 

described, which was collected in an African thermal spring. 

Italy hosts four species - three of which are endemic to the country - living in 

saturated aquifers. Limnosbaena finki is found in karstic and alluvial water in 

north-eastern Italy (it is distributed as far as Bosnia); Monodella stygicola only 

lives in karstic habitats, occasionally in alluvial aquifers, in Apulia; Tethysbaena 

argentarii is an endemic species of anchialine waters in the Grotta di Punta 

degli Stretti (Argentario Promontory, Tyrrhenian), and Tethysbaena siracusae is 

endemic to the karstic area of Porto Palo in south-eastern Sicily. 

Spelaeomysis bottazzii (ca. 1x) 

■ Mysidaceans 

Mysidaceans, or opossum shrimps, are 

malacostracans generally living in sea 

or brackish water. In Italy, there are two 

stygobiont genera, Stygiomysis and 

Spelaeomysis, in anchialine and 

freshwater in karstic areas in Apulia. 

The Mediterranean area hosts a third 

stygobiont species, Troglomysis, in the 

Dinaric karst. These detrivorous and saprophagous animals are 2-3 cm long - 

thus, unusually large compared with other mysids - and are found in small 

lakes, seldom in flowing water. 

A euryhaline and eurythermal species, Spelaeomysis bottazzii, usually lives in 

anchialine habitats in south-eastern Italy, between the Gargano and Salento 

(Apulia), even in polluted water. Stygiomysis hydruntina is rare, and 

presumably lives further down, where the water-table recharges; so far, it has 

only been collected on the Ionian side of the province of Lecce. The two 

species may locally cohabit. Although electrophoretic analyses suggest that 

the species are of recent, perhaps Pliocene origin, similar species in Mexico, 

the Caribbean and eastern Africa imply a more ancient, Tethyan origin. 

■ Isopods 

Woodlice are a very diversified order 

of malacostracan crustaceans, with 

more than 10,000 known species. 

They presumably colonised Italian 

groundwater from marine (cirolanids, 

microparasellids, microcerberids) 

and surface freshwater ancestors 

(asellotans and perhaps sphaeromatids). 

Each family is a microcosm in itself, 

Proasellus franciscoloi (ca. 6x) 

and their study reveals very interesting 

biogeographical aspects. 

Asellids. Almost all stygobiont species of this family are Italian endemics. 

Asellus cavernicolus lives in the river Timavo (Trieste Karst). Results from 

molecular studies reveal that it is a relict species deriving from pre-glacial 

colonisation of the Trieste Karst by an epigean species, Asellus aquaticus. In 

Italy, the genus Proasellus counts several surface as well as cavernicolous 

and interstitial species. 

The genus diversified into many phyletic lines, the taxonomy of which 

requires clarification: the group deminutus in north-eastern Italy; pavani in the 

central-eastern Pre-Alps; cavaticus in France, western Piedmont and Liguria, 

in karstic environments (P. cavaticus, P. franciscoloi), and the group patrizii, 

exclusive to Sardinian groundwater. In addition, there are many similar 

species: P. ligusticus, found from Liguria to the Apuan Alps, and P. acutianus, 

in Tuscany, Latium and the island of Elba are the most widely distributed 

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62 

species. Other species are only known to live in restricted areas, like P. 

amiterninus, P. dianae, P. adriaticus and P. faesolanus. 

The similar genus Chthonasellus includes C. bodoni, endemic to karstic and 

interstitial waters in the Cuneo area (Piedmont), which is thought to be 

phylogenetically close to the French genus Gallasellus. 

Stenasellids. This family comprises exclusively stygobiont species of very 

ancient origin, found in Tuscany (Stenasellus gr. racovitzai) and Sardinia, in 

both caves and interstitial habitats. In Sardinia, techniques of molecular 

biology have identified many endemics, two of which have so far been 

attributed to S. racovitzai and are similar to French species, and two others 

(S. nuragicus, S. assorgiai) are similar to species found in eastern Europe. 

Two species collected in the area of Nuoro (Sardinia) are similar to Spanish 

species. 

Preliminary dating based on “molecular clocks”, suggests that the separation 

of the two phyletic lines dates back about 28 million years (Upper Miocene). 

This is one of the most fascinating biological pieces of evidence of the 

complex Tyrrhenid history. 

Microparasellids. This family of tiny isopods (a few mm long) deriving 

from ancient marine ancestors which colonised interstitial habitats 

during the marine regressive phases. Their distribution follows the 

ancient coastline of Tertiary seas. In Italy, six interstitial species are 

known, all belonging to the genus Microcharon (see drawing). Of 

these, only M. marinus is associated with transient groundwater 

along the Mediterranean coasts, and the geographical location of 

other species - e.g. M. novariensis, found in Piedmont springs - 

reveals that they are relicts. 

Microcerberids. The family comprises mainly marine species, and only 

the relict Microcerberus ruffoi (see drawing) lives in Italian underground 

freshwater (water-table of the river Adige). 

Cirolanids. This family includes mainly marine species, and only 

two are Italian stygobionts. Sphaeromides virei inhabits alkaline 

water in the Gorizia Karst. A voracious predator, it is quite large (more 

than 3 cm long). Its typically Balkanic distribution and fragmentation 

into endemic subspecies suggest that it originally lived in 

groundwater in the Dinaric karst. Typhlocirolana aff. moraguesi is 

exclusive to the karstic system near Porto Palo (Siracusa, Sicily), 

and was distinguished from T. moraguesi (island of Majorca) with 

molecular biology techniques. Its origin is probably palaeo- 

Mediterranean. 

Sphaeromatids. Many species of the genus Monolistra, widely distributed in 

the Balkans, also live between the Italian-Slovenian border and the area of 

Como (north of Milan), in karstic groundwater in Pre-Alpine caves. Their 

absence north of the line that marked the southern boundary of the great 

Quaternary glaciers shows that they settled in groundwater during the 

Pliocene, perhaps deriving from surface freshwater ancestors which have 

become extinct. 

Ongoing molecular research will clarify their evolution. Each species and 

subspecies is endemic to a restricted karstic system. Monolistra 

schottlaenderi is exclusive to saturated aquifers of the Karst in the areas of 

Trieste and Isonzo, and is the only Italian member of the subgenus 

Microlistra, which also lives in Slovenia and Croatia. The species of this 

subgenus have knobby dorsal protrusions, and sometimes even long, robust 

spines that function as efficient defensive structures when the animal curls 

into a ball. 

Among other species, with smooth teguments, there is Monolistra julia, 

endemic to caves in the Julian Pre-Alps, where it lives in small streams of 

trickling water. It has two well-developed caudal appendages (uropods). Other 

species do not have uropods, which may be atrophic or barely visible. The 

furthest west (Monolistra pavani) is found in the underground stream of the 

Buco del Piombo (Como). 

Monolistra racovitzai (ca. 5x) 

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Species of genus Niphargus; top: N. costozzae; centre: N. longicaudatus; left, bottom: N. pescei (top) 

and N. transitivus (bottom); right, bottom: N. bajuvaricus grandii (ca. 3x) 

■ Amphipods 

This order of malacostracans includes 

several marine and freshwater species, 

sometimes sub-terrestrial, which 

colonised groundwater either directly 

from the sea, or from ancestors that 

once inhabited limnic surface water. In 

Italy, there are about 100 stygobiont 

species, almost all of which are 

endemic. 

Bogidiellids. Italian freshwaters host 

seven stygobiont species, most of Bogidiella sp. (ca. 10x) 

which are interstitial, occasionally 

euryhaline. Bogidiella albertimagni (in the Po Plain) and Bogidiella aprutina are 

the only continental species; the others are Tyrrhenian endemics, found in 

Sardinia and on the island of Elba. 

Gammarids. This family comprises exclusively surface species. Among those 

which only live in groundwater and are Italian endemics, two species of 

Tyrrhenogammarus live in karstic aquifers in south-eastern Sicily 

(Tyrrhenogammarus catacumbae) and Sardinia (T. sardous). One species of 

Longigammarus (L. planasiae) has recently been collected from a well on the 

limestone island of Pianosa (Tuscan archipelago), and a specialised species, 

Ilvanella inexpectata, is known to inhabit alluvial aquifers on the island of Elba 

and in Tuscany. 

Hadziids. The genus Hadzia - presumably a Tethyan relict - has four Italian 

species. Hadzia fragilis stochi, an endemic subspecies with delicate, elongated 

appendages, has been described in alkaline water in the karstic area of Trieste 

and river Isonzo. Hadzia minuta inhabits karstic waters in Salento, and H. 

adriatica has been collected from pools in Apulia. Another species, which is 

still under description, was recently found in southern Sardinia. 

Niphargids. The genus Niphargus (more than 250 known species, 70 of which 

live in Italy; size between 3 and 40 mm) have complex, controversial 

taxonomy, which is currently being revised by means of molecular biology 

techniques. Their distribution area includes most of Europe (except for the 

Iberian Peninsula and the upper northern areas) and stretches east towards 

Iran. This suggests that the genus colonised European surface freshwater 

from the basins of the Tertiary Paratethys, and later moved into groundwater. 

However, fossils similar to present species have recently been found in Baltic 

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66 

amber, implying a perhaps more ancient origin. Almost all species are endemic 

and live in the Alps and Po Plain, in several distinct, although not welldefined 

phyletic lines (the main groups being stygius, kochianus, aquilex and 

bajuvaricus). 

The diversity of the genus decreases proceeding southwards down the 

Apennines, with species belonging to the groups speziae (northern and 

central Apennines), longicaudatus (throughout the Apennines, Sicily, 

Sardinia, and smaller islands), and orcinus. This last group includes species 

similar to Balkan ones (exclusively associated with karstic aquifers), which 

colonised Italy from the Julian karst in the north-east and, perhaps through 

trans-Adriatic pathways, the limestone systems of the central-southern 

Apennines and Apulia. In addition to these groups, there are several species 

of unknown affinity, like Niphargus stefanellii (found in caves in centralsouthern 

Italy), which seems related to Balkan species, and colonises even 

sulphureous waters. 

Niphargus species, which are greatly diversified in structure and size, 

colonise all types of underground habitats. In large alkaline karstic lakes, 

species are large (2-4 cm) with elongated antennae and other appendages, 

and large anterior claw-shaped limbs (gnathopods) for seizing prey 

(Niphargus steueri, N. tridentinus). Interstitial environments host small 

omnivorous species (3-10 mm) with globose (Niphargus pupetta, N. 

transitivus) or elongated, worm-like bodies (Niphargus bajuvaricus grandii, 

N. italicus). Other species colonise subsurface, non-karstic aquifers, and 

may even be found in moist soil. They have tapering bodies, like N. 

dolenianensis and various species of the group longicaudatus. Italy also 

hosts the only species of the related genus Carinurella (C. paradoxa), which 

has a globose body with stumpy appendages and lives in interstitial waters of 

Friuli Venezia Giulia. 

Salentinellids. This is possibly a palaeo-Mediteranean amphipod family that 

comprises only stygobionts deriving from marine ancestors, whose identity is 

still uncertain. 

Salentinella species are still undergoing revision, and the most common 

species, S. angelieri, is typically interstitial and lives in brackish water near the 

coastline. It is also found in caves of isolated karstic systems and in true 

continental groundwater, with other species like S. franciscoloi of Liguria. 

Salentinella gracillima is exclusive to groundwater in Apulia. 

Ingolfiellidae. This family includes many stygobionts with elongated bodies 

living in marine and freshwater interstitial environments. So far, only one 

species has been found in Italian fresh groundwaters: Ingolfiella 

(Tyrrhenidiella) cottarellii, from a cave on the island of Tavolara (off the northeastern 

coast of Sardinia). 

Metaingolfiellids. The family comprises the single species Metaingolfiella 

mirabilis, which is quite large (3 cm). Many specimens of this species were 

collected, on a single occasion, from water pumped out of a deep karstic well 

in Salento. Described in 1969, it has never been found since. It is perhaps one 

of the most ancient palaeo-endemics of Italian fauna. Its body structure and 

the shape of its gnathopods suggest that it is a predator. 

Pseudoniphargids. This family includes only stygobionts, and is particularly 

diversified in the Mediterranean area. In Italy, only a few species are known, 

living in interstitial environments and caves near the coastline, showing their 

marine origin. Two species (Pseudoniphargus africanus italicus, P. sodalis) live 

in Sicily, and one (P. planasiae) in the Tuscan archipelago. Pseudoniphargus 

adriaticus has been collected in wells near Bari, and is also known to inhabit 

the Pelagian Islands (between Sicily and Tunisia), although its taxonomic 

status is uncertain. Other specimens, collected in Sardinia, are still being 

examined. 

Metacrangonyctids. This family is distributed around the Atlantic, includes only 

stygobionts, and is very diversified in the Mediterranean area. Italy hosts only 

Metacrangonyx ilvanus, endemic to the island of Elba, where it was recently 

found only in one well in alluvial groundwaters. 

Salentinella angelieri (ca. 30x) 

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■ Decapods 

Italian fauna has only two stygobiont 

decapod genera living in karstic waters: 

Troglocaris (Isonzo and Trieste Karst) 

and Typhlocaris (Apulia). Recent 

research has revealed that Italian caves 

actually host two species of shrimps of 

the genus Troglocaris of the 

anophthalmus group, morphologically 

difficult to distinguish, but easily 

Troglocaris anophthalmus 

identified by means of molecular 

biology techniques. They may belong 

to T. anophthalmus (Gorizia Karst) and 

T. planinensis (Trieste Karst), although 

their taxonomy still requires 

Typhlocaris salentina 

confirmations. Stygobiont species of 

the genus Troglocaris were thought to 

derive from marine ancestors. Very 

recent molecular biology analyses 

carried out at the University of Ljubljana 

(Slovenia) have dated the separation of 

the western anophthalmus group from 

the Dinaric-Caucasian one at between 

6 and 11 million years ago, and the 

beginning of speciation within the 

anophthalmus group between 3.7 and 

5.3 million years ago. Their marine origin is therefore very ancient, and 

populations colonised groundwater coming from surface freshwater. 

The third species of Italian stygobiont decapods, Typhlocaris salentina, is 

endemic to Apulian caves. It was discovered in the Grotta Zinzulusa at Castro 

Marina in 1922, and later collected from other caves in Salento, Murge and 

Gargano. This blind, depigmented prawn may reach exceptional sizes (up to 

13 cm); a predator, it feeds on mysidaceans and stygoxene organisms. 

The genus Typhlocaris includes two stygobiont species living in groundwater 

in Israel and Libya, suggesting that it is an ancient relict of an otherwise extinct 

palaeo-Mediterranean pre-Pliocene surface fauna associated with a subtropical 

climate. Unfortunately, molecular data on this genus are not yet 

available. 

■ Amphibians 

The olm (Proteus anguinus) is the only stygobiont amphibian of the Palaearctic 

fauna. The pétit dragon of the Postojna caves (Slovenia) - discovered by the 

Slovenian nobleman Valvasor in 1689 and briefly described by Laurenti in 

1768 - is the best-known underground animal described so far and, in some 

ways, the most fascinating. It has a pinkish-white eel-shaped body, with 

atrophic eyes concealed under the skin and outer red gill plumes which it 

retains throughout its life. The olm is known for its neoteny, i.e., it reaches 

precocious reproductive maturity despite its larval appearance. Olms are 

predators feeding on other aquatic, even stygoxene animals; the females lay 

between 20 and 80 eggs, one at a time for over one month, and place them 

under rocks and stones. The greyish tadpoles have distinct eyes, which they 

retain until they are two months old. Until the age of three months, olms feed 

exclusively on yolk stored in the cells of their digestive tracts. In nature, 

reproduction seldom occurs before the tenth year of age. 

The origin of olms is debated. Fossils of proteids and iguanodonts, found at 

Bernissart in Belgium, date back to the Lower Cretaceous, when olms lived in 

surface water. Their colonisation of karstic groundwaters in the Dinaric area 

where they now live may have started in the Pliocene, when karstification 

began. In 1994, in the Slovenian Karst, a pigmented, eyed subspecies was 

Olms also live in the groundwaters of the Isonzo Karst 

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Olm (Proteus anguinus) 

discovered (Proteus anguinus parkelj) 

genetically similar to the stygobiont 

populations of the same area, and 

thus suggesting that groundwater 

populations are more recent. 

Recent molecular analyses reveal that 

there may be more stygobiont olm 

species. 

In Italy, olms are known to inhabit only 

alkaline water in caves of the Trieste 

and Isonzo Karsts. An isolated 

population, introduced from Slovenia 

in 1850, still lives in Grotta Parolini at 

Oliero (Vicenza). 

Olms are the only Italian stygobionts 

listed as priority species in the Habitats 

Directive; they are also included in 

Annex IV and are therefore under strict 

protection. 

■ Italian stygofaunal provinces 

Some olm specimens, coming from Slovenia, 

were introduced into the Oliero cave system 

(Veneto) in 1850 

As analysis of previously described taxonomic groups suggests, the present 

geographical distribution of stygobiont species in Italy is the result of a series 

of events which took place in ancient times (historical factors) and, to a lesser 

extent, of ecological factors, which occour in “real time”. The role played by 

both is described in the chapter on ecology. 

Since the evolution of many Italian taxonomic groups was similar over time, 

because they were affected by the same palaeogeographical events, Italy is 

divided into areas with similar fauna, particularly endemics. These areas are 

called stygofaunal provinces. Although these generalisations cannot tell us 

directly what the present fauna composition of a specific aquifer is, because 

this is also influenced by local events, they do describe the present situation 

of Italian stygobionts and explain where the most important endemic 

locations are found. 

Dinaric province. This area includes only the easternmost portion of Italy - 

the so-called “classic” Karst - an elliptical area of 200 km 2 , whose 

stygobionts are similar to those of the Karst in Slovenia, Istria and Dalmatia. 

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Stygofaunal provinces in Italy 

The area was affected by karstification 

in the late Miocene, and hosts many 

palaeo-endemics. Exclusive to the 

karstic vadose zone are harpacticoid 

copepods of the genus Morariopsis, 

the bathynellacean Bathynella 

skopljensis and the amphipod 

Niphargus stygius. 

Exceptional fauna, whose western 

limit of distribution is the Karst, 

populates large cavities filled with 

alkaline karstic water. 

Among these, there are polychaetes 

(Marifugia cavatica), gastropods 

(Belgrandia stochi), ostracods (Cypria 

cavernae), calanoids (Troglodiaptomus 

sketi), and several cyclopoids and 

Sphaeromides virei (ca. 1x) 

harpacticoids (like Acanthocyclops 

troglophilus and Nitocrella stochi). This area hosts the only Italian stygobiont 

isopods of the genus Asellus, those of the subgenus Microlistra, and the large 

Sphaeromides, as well as amphipods, which are highly diversified, with many 

endemics (e.g., Niphargus stochi, Hadzia fragilis). Other remarkable 

inhabitants are decapods of the genus Troglocaris, and the most famous 

stygobiont species, the olm (Proteus anguinus). Aquifers in marl and 

sandstone also host very interesting fauna, with very different species from 

those found in adjacent karstic aquifers. Among the main biogeographical 

markers, there is the gastropod Istriana mirnae, and the large amphipods 

Niphargus spinulifemur and N. krameri. 

Alpine province. The Alpine stygofaunal province includes a very complex 

area associated with Alpine orogenetic events. It is divided into a northern part 

(strictly Alpine), above the southern limit of the great Quaternary glaciations, 

and a southern Pre-Alpine one, below which is the recent alluvial area of the 

Po Plain. The Alpine area is populated by only a few stygobionts: cold-loving, 

stenothermal species which followed the retreat of Quaternary glaciers and 

colonised aquifers in carbonate and crystalline rocks in the Alps. In particular, 

a number of amphipods (Niphargus forelii, N. similis, N. strouhali) even live at 

high altitudes, above 2000 m, together with a few copepods and 

bathynellaceans. 

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In the Pre-Alps, the situation changes completely, as there are large numbers 

of endemics living in the numerous karstic systems. The main 

biogeographical component is of eastern origin and stretches westwards as 

far as the Pre-Alps near Como, with a few genera living on Mount Fenera 

(Piedmont) (hydrobioid gastropods of the genus Iglica, harpacticoids of the 

genus Paramorariopsis). Typical genera of this area are several hydrobioids 

(Bythiospeum, Hauffenia, Hadziella, Iglica, Paladilhiopsis), harpacticoids 

(Lessinocamptus, Paramorariopsis, and several species of the genus 

Elaphoidella), amphipod crustaceans (Niphargus of the stygius group) and 

isopods (Monolistra, Proasellus). The western and Ligurian Pre-Alps have 

fewer stygobionts, and their fauna is more similar to that in France (Proasellus 

of the cavaticus group) and the Apennine province (Alzoniella, Niphargus of 

the longicaudatus group). 

Padanian province. The alluvial areas of the Po Plain, which stretch into the 

Alpine and Apennine valleys, have many endemics. Here, as in the nearby 

Alpine province, there are many species from the east, such as the isopod 

Proasellus intermedius, and several endemic amphipods (Niphargus italicus, 

N. pupetta, N. transitivus, N. longidactylus, Carinurella paradoxa). Other 

species are associated with the fauna of the extensive plains of centraleastern 

Europe, and probably migrated towards Italy in more recent times, like 

several cyclopoids of the groups languidus and languidoides of the genus 

Diacyclops, the bathynellacean Anthrobathynella stammeri, and the 

amphipods Bogidiella albertimagni and Niphargus bajuvaricus grandii. There 

are also more ancient organisms of pre-Quaternary marine origin, relict 

species survived to Pliocene events, perhaps also to Miocene sea retreat, like 

the recently discovered ectinosomatid harpacticoids and isopods of the 

genera Microcerberus and Microcharon. 

Apennine province. Despite its extent, from the Colle di Cadibona (Savona) to 

the Madonie in Sicily (excluding Apulia), the fauna of this area is well 

characterised. There are areas rich in endemics (Ligurian Apennines, Alburni 

mountains, Gran Sasso Massif) that are widely distributed in the Apennines. 

The apparent monotony of this fauna may be related to historical events, as 

karstification here is a recent event, and the fragmented limestone outcrops in 

the Apennines were covered by little permeable soil in the interval between the 

Pliocene and Miocene, and were only uncovered in the Quaternary. These 

palaeogeographical events are very similar from Latium to Calabria, and the 

areas are inhabited by endemics which are found along the Apennines and do 

not have particular habitat preferences (cyclopoid copepods of the genus 

Diacyclops, harpacticoids like Attheyella paranaphtalica and Nitocrella 

stammeri, and the amphipod Niphargus longicaudatus, which live in recent tufa 

Diacyclops gr. languidus, females with egg-sacs (ca. 70x) Harpacticoids of the genera Lessinocamptus (left) and Paramorariopsis (right) (ca. 100x) 

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aquifers in the Sabini mountains and in 

karstic water in Cilento and evaporites 

in Calabria as well). These recent 

populations settled where palaeoendemics 

were already living and 

characterised Apennine areas. Thus, 

groundwater percolating in Triassic 

evaporites in Emilia hosts Niphargus 

poianoi; the karstic systems of the 

Aurunci, Gran Sasso and Alburni 

ranges are inhabited by the 

extraordinary copepod Acanthocyclops 

Stygiomysis hidruntina (ca. 2x) 

agamus and species of the genus 

Pseudectinosoma, which are perhaps 

Messinian relict. As regards gastropods, the genera Alzoniella, Avenionia and 

Fissuria live in the northern Apennines, and Arganiella, Orientalina and 

Pauluccinella in the central Apennines; the genus Islamia is divided into 

northern and central-southern species. 

Apulian province. Apulian groundwater is clearly different from that of the 

Apennines, and is rich in specialised endemics, especially in often brackish, 

saturated, karstic habitats. This is due to the extent and ancient origin of 

karstification, as well as to the geological history of Apulia, which palaeogeographers 

consider as part of a different tectonic micro-plate from those 

that shaped the Italian peninsula. These waters host exceptional specialised 

organisms of marine origin, like the sponge Higginsia ciccaresei, the 

gastropod Salenthydrobia ferrerii, the ostracods Trapezicandona stammeri 

and Pseudolimnocythere hypogea, the thermosbaenacean Monodella 

stygicola, the extraordinary metaingolfiellid amphipod Metaingolfiella 

mirabilis, the hadziid amphipod Hadzia minuta, the salentinellid Salentinella 

gracillima, mysids of the genera Spelaeomysis and Stygiomysis, and the large 

decapod Typhlocaris salentina. 

Tyrrhenian and Sardinian provinces. This province includes Sardinia, part of 

the Tuscan archipelago and isolated coastal areas in Italy deriving from the 

fragmentation of the Tyrrhenid, which started in the Oligocene. Palaeo- 

Tyrrhenian endemics are phylogenetically similar to evolutionary lines in the 

areas of Provence, the Pyrenees and Corsica. Among the several Sardinian 

endemics, the gastropod genera Sardhoratia and Sardopaladilhia, many 

species of cyclopoid and harpacticoid copepods, the bathynellacean 

Sardobathynella, the entire phyletic line of isopods related to Proasellus patrizii, 

and isopods of the genus Stenasellus, are also found along the Tuscan coast. 

Also presumably of palaeo-Tyrrhenian origin are the thermosbenacean 

Tethysbaena argentarii of Mount Argentario (Tuscany) and the amphipod 

Metacrangonyx ilvanus of the island of Elba. Other animals associated with local 

anchialine water are many amphipods of marine origin of the genera Bogidiella 

and Pseudoniphargus, and the subgenus Thyrrenidiella of genus Ingolfiella. 

More doubtful are the relationships between some gammarid genera, like 

Longigammarus, Tyrrhenogammarus, and the puzzling Ilvanella. 

Iblean province (Sicily). Sicilian stygobionts are biogeographically composite 

and little known, especially those living in the alluvial plains and karstic 

aquifers that sometimes develop in chalk. Clearly identified organisms are 

found in the Iblean area, especially in the water-table of the karstic system 

near Porto Palo. Although this small area is jeopardised by man-made 

alterations, exceptional, perhaps palaeo-Mediterranean endemics inhabit it, 

like the thermosbaenacean Tethysbaena syracusae, the cirolanid isopod 

Typhlocirolana aff. moraguesi, and the amphipods Tyrrhenogammarus 

catacumbae and Pseudoniphargus duplus. 

Examples of distribution of endemic stygobiont species; left: gastropods of the genus Paladilhiopsis 

(Eastern Pre-Alps, red circles) and Arganiella (Apennines, green circles); right: crustaceans of genera 

Stenasellus (Tyrrhenian, red circles), Spelaeomysis (Apulia, blue circles) and Tyrrhenogammarus 

(T. catacumbae, Iblean Mts, Sicily, green circles) 

77

Ecology 

DIANA MARIA PAOLA GALASSI 

Although Stygobiology - the science 

that studies groundwater biology - 

dates back to the 18th century, it was 

only in 1994 that the ecological 

importance of this environment was 

finally acknowledged and exhaustively 

described in the monograph 

Groundwater Ecology (see select 

bibliography). No matter how surprised 

we may be to learn that findings in 

groundwater ecology are recent, our 

surprise turns to shock on hearing 

that, although groundwater protection 

and management are of paramount 

importance for human survival, current 

legislation does not take into account 

the ecology of this particular 

Bottom of an old well for drinking-water 

environment. 

This is probably due to the unique characteristics of groundwater: invisible to 

most, not perceived as part of the territory, a totally dark world populated 

almost exclusively by tiny creatures. The biodiversity of this environment is 

truly “hidden”, as the subtitle of this volume suggests. This is perhaps the 

reason, albeit not a justifiable one, why man, in both law and culture, has 

always considered the exploitation of groundwater as more important than its 

ecology. It is a narrow-minded view, as we realise when reading the previous 

chapter on the complexity, diversity and scientific importance of stygofauna. 

It therefore comes as no surprise that, while there are only a few books to 

describe the geological and speleological aspects of these habitats, almost 

none has yet been published in Italy on underground ecology. This chapter is 

an attempt at overcoming the anthropocentric view of groundwater, at 

illustrating how the ecosystem works, and analysing the ecological factors 

that regulate the structure of groundwater communities and biodiversity. 

Waterfall produced by the karstic spring of Col del Sole (Friuli Venezia Giulia) 

79

80 ■ The ecology of aquifers 

According to their hydrogeological and hydrological characteristics, aquifers 

are divided into three groups. 

Karstic aquifers are the most intensively studied from the biological 

viewpoint, perhaps because caves allow scientists easy access to them. 

These aquifers develop in large bedrock cavities, generally limestone, 

through a complex network of micro-fissures formed by the dissolution of 

carbonates. 

This group includes waters that penetrate chalk, and that flow into 

conglomerate, in which dissolution acts on evaporites and the cementing 

matrix of breccia and puddingstone. In the hydrological cycle, karstic 

aquifers undergo great variations in flow and, therefore, from the ecological 

viewpoint, they are less predictable systems. 

Unsaturated (vadose) karstic systems, which are more directly influenced by 

rainfall, are less stable than saturated ones. However, the stability and 

predictability of saturated karstic systems in turn depend on the age and 

depth of aquifers. Generally, ancient, deep aquifers are ecologically more 

stable than young, shallow ones. 

Sketch showing the three main types of aquifers: fractured lithoid (A), porous (B), karstic (C) Hypotelminorheic habitat 

Porous and alluvial aquifers develop in unconsolidated sediments where 

interstices between sediment particles vary according to the particle size of 

the sediment itself. 

Porous aquifers may be divided into unsaturated or semi-saturated and 

saturated (water-tables). Medium-fine porous aquifers have greater physical 

inertia and, as water lasts in them for longer than in karstic aquifers, they are 

ecologically more stable and predictable. 

In non-karstic lithoid (stone) aquifers, water circulates in fractures (as in 

crystalline rock), between layers (marl-sandstone in flysch facies) and 

cavities of other origin (e.g., the lava flows of Mt. Etna). Water percolates in 

fissures whose size depends on the events that created them, and on the 

solubility and erodibility of rocks. 

Practically unknown from the ecological viewpoint, these aquifers are very 

similar to karstic ones if their fractures or cavities (as in lava tubes) are large, 

or behave like porous ones in the surface cortex, where soil and 

disintegrated rock host communities typical of porous systems. 

Lastly, a particular mountain environment is found in leaf litter with trickling 

water underneath, the so-called hypotelminorheic habitat. This does not 

represent a true aquifer, but is surface water flowing a few centimetres deep. 

81

82 

Although the ecology of this unsaturated habitat is similar to that of porous 

surface aquifers, it is very unstable and unpredictable. 

Organisms from adjacent and underlying aquifers may migrate to these 

habitats to feed. 

The same aquifer often hosts more than one of the above categories: for 

instance, there are streams in cavities between flysch and limestone (in 

Friuli Venezia Giulia), between limestone and conglomerate (Veneto Pre- 

Alps), travertine and tuff (Latium), limestone and chalk (Grotte di Frasassi), 

limestone and lava (Lessini mountains), and limestone and granite 

(Sardinia). 

In addition, the water of karstic aquifers often drains to alluvial beds in 

valleys with complex hydrogeological and ecological relationships. 

■ Groundwater habitats 

The main ecological aspect deriving from the classification described above 

is that the various types of aquifers provide fauna with a complex availability 

of living space, with changes in structural complexity, food resources, 

stability of hydraulic conditions and water chemistry. Basically, different 

aquifers develop different habitats, and may host completely different 

animals. 

For instance, locally or extensively saturated karstic aquifers often have 

large hydric spaces (underground rivers or lakes), and therefore contain 

larger organisms which may reach a few centimetres in size, like large 

cirolanid isopods, mysids, decapods and the olm, the only Italian stygobiont 

vertebrate. 

Unsaturated karstic environments host smaller animals because the pools in 

caves - large pools or lakes of trickling water - are only transient habitats for 

fauna living in limestone micro-fissures above, adjacent to or underneath the 

pools. 

Medium-fine porous aquifers provide little living space, and only small 

animals - less than 1 cm long, often smaller than 1 mm, according to the 

size of particles - with particular adaptations have been able to colonise 

them. 

Fractured aquifers, in line with their nature, may offer different extension of 

living spaces, and therefore host relatively large animals (in flysch, amphipods 

of the genus Niphargus are up to 4 cm long) as well as microscopic organisms 

typical of porous systems. 

Unsaturated karstic habitat (micro-concretions) Porous habitat with (detail) a specimen of Niphargus in its environment 

83

84 85 

The discovery of a new submerged world: anchialine environments 

Diana Maria Paola Galassi 

Anchialine environments were first 

discovered in 1966, when the Austrian 

scientist Rupert Riedl described them 

as “marginal caves”. Since then, 

experts have debated the correct 

definition of anchialine systems. Today, 

they agree on defining them as caves 

or other underground aquatic habitats 

near the coastline of islands and 

continents, supplied by continental 

freshwater and with underground 

connections to the sea. Consequently, 

the water of anchialine pools is 

brackish, and light-weight freshwater 

generally floats on top of heavier 

seawater. 

The most typical feature of anchialine 

environments is the absence of a 

surface connection with the sea, which 

manages to reach far inland through 

deep infiltration passages in limestone 

and volcanic rocks. 

The most fascinating, extraordinary 

examples are the well-known Mexican 

cenotes, small bodies of crystalline 

brackish water, like blue eyes glittering 

in the tropical forests of Mexico and 

Belize, not far from the coast. In Italy, 

typical anchialine pools are found in 

the Grotta Zinzulusa, Abisso and Buco 

dei Diavoli (Salento), together with 

other water-tables in Apulia, 

groundwater in Porto Palo (Sicily), the 

Grotta Verde, Grotta di Nettuno and 

Grotta del Bue Marino (Sardinia) and 

the Grotta di Punta degli Stretti 

(Argentario, Tuscany). 

Anchialine pools are marked by few 

food resources, total darkness, and 

vertical gradients of salinity and 

oxygen concentrations. Although in the 

past anchialine ecosystems were 

believed to support themselves on 

allochthonous organic matter (deriving 

from the rock above and from 

seawater), today we know that part of 

the organic matter is locally 

synthesised by chemo-autotrophs. 

The most fascinating aspect that 

makes these environments true treasure 

troves of biodiversity is their exclusive 

fauna. Examples are remipedes, the 

most primitive class of living 

crustaceans, which have been found in 

anchialine caves on the Bahamas, in 

lava tubes on the island of Lanzarote 

and, more recently, in Australia. 

Remipedes, like many other animal 

groups found in these habitats, are true 

living fossils, whose distribution, 

enigmatically uneven in several areas 

of the world, dates back to the breakup 

of the ancient Tethys Sea. 

In addition to these unique organisms, 

there are also other extraordinary 

animals, some of which are Italian 

endemics with restricted distribution, 

like the sponge Higginsia ciccaresei, 

the thermosbaenacean Monodella 

stygicola, the mysid Stygiomysis 

hydruntina, and the decapod 

Typhlocaris salentina. 

It is worth noting that the copepod 

Muceddina multispinosa was recently 

discovered in the Grotta Verde (Capo 

Caccia, Alghero, Sardinia), a species 

with disjunct distribution also found in 

anchialine environments on the islands 

of Mallorca and Lanzarote (Spain). 

Generally speaking, anchialine habitats 

host heterogeneous assemblages 

which includes strictly marine animals 

and, to a lesser degree, freshwater 

organisms. 

Typically anchialine species are closely 

associated with the particular 

environment in which they live, and 

have never been found in other types of 

underground habitats. They are also 

stygobionts, and have marked 

specialised features. Their origin dates 

back to various geological times, from 

the Tertiary to the more recent 

Sea entrance to the Grotta Zinzulusa (Salento, Apulia) 

Pleistocene. Some researchers believe 

that their ancestors lived in the abysses 

of the sea; others trace their origin back 

to organisms living in shallow seawater 

on the continental shelf.

86 

The Fontanon di Goriuda drains the karstic plateau of Mt Canin (Julian Pre-Alps, Friuli) 

Simplified sketch of a karstic aquifer 

■ Ecology of karstic aquifers 

The network of karstic conduits has two components that offer different living 

conditions to fauna: transmissive and capacitive components. The transmissive 

component is typical of highly karstified systems with great hydraulic 

conductivity and fast currents and, ecologically speaking, has little biodiversity. 

What kind of species could possibly survive in such hostile environments? Yet 

some actually can, and have even been incredibly successful in adapting to 

these harsh habitats. For example, some amphipod crustaceans of the genus 

Niphargus have evolved adaptations to exploit the advantages of fast currents 

in habitats where interspecies competition is very low. 

Research carried out in France reveals that these species, which perhaps live 

in fissures adjacent to the transmissive/drainage conduit, lay their eggs 

nearby, and exploit the speed of the current to disperse their young. Briefly, 

they synchronise their biological cycle to the discharge of the aquifer while 

developing growth strategies typical of changeable habitats: thus, they 

produce large numbers of fertilised eggs, a few of which will reach the adult 

stage, in ways which are typical of surface species rather than underground 

ones. Some species of isopod crustaceans of the genus Monolistra also 

exploit fast currents by curling up into balls and letting themselves be 

transported over great distances. 

In capacitive karstic systems, whose development varies according to the 

aquifer, water percolates in medium-sized and small fractures in branching 

87

88 

anastomoses, often adjacent to the main drainage system. Here, they form 

small pools of calm water which are connected to one another and flow into 

the main drainage conduit. This lateral network, which is generally more 

extensive and has greater volume than the drainage one, is called the 

capacitive annex system. Unlike the drainage system, which poses a severe 

threat to the survival of species, the situation is completely reversed in the 

capacitive system, where water flows slowly and there are large amounts of 

organic matter and inorganic sediments, creating habitats for many 

underground species. Biodiversity may even increase in capacitive systems 

with wide, diversified living environments, like underground lakes. Only in 

these habitats do we find plankton (calanoid copepods) together with benthic 

and interstitial organisms, large predators, like cirolanid isopods, large 

decapod crustaceans, and the olm. 

Unsaturated karstic systems also have a diversified network of storage microfractures, 

where living conditions are favoured by the three-dimensional 

complexity of the system. The diversity of substrates in small pools of water 

(pools and puddles with silt, clay, sand and organic material percolating from 

the surface, or complex calcium microstructures) give rise to diversified fauna, 

even if temporary water circulation prompts species to devise adaptations to 

withstand adverse conditions in small, locally saturated fractures. 

■ Ecology of alluvial aquifers 

Sketch illustrating connection between transmissive system and capacitive annex subsystem during flood and 

drought periods Gravel bed of the Tagliamento (Friuli Venezia Giulia) 

The habitats of saturated porous aquifers are not very heterogeneous, and 

conditions are determined by the size of sediment grains in unconsolidated 

sediments. Food is restricted, because most of the organic matter coming 

from the surface is trapped in the subsurface layers of aquifers. 

The opposite is observed in surface unconsolidated sediments, generally 

unsaturated, where the surface aquatic and terrestrial environments are 

continuous or adjacent, giving rise to heterogeneous habitats due to the 

ecotonal nature of these environments and the greater availability of organic 

matter. 

Proximity to wet or dry surfaces produces greater concentrations of organic 

matter than in deeper saturated layers, thus contradicting the now out-dated 

idea that underground habitats lack niches and habitats. 

The hyporheic environment (where groundwater and surface water mix) is 

perhaps the most typical example of a subsurface alluvial aquifer and is, 

among underground habitats, certainly the best-known from the ecological 

viewpoint. It is an ecotone, that is, a transitional area between the surface 

habitat of running water (stream or river) and the saturated underground 

habitat (groundwater). 

89

90 

Literature defines this environment in myriad ways, each a nuance of the 

other, the only differences being the thickness attributed by each expert to 

the hyporheic layer. Aquatic ecotones are areas in which large-scale hydraulic 

exchanges occur and where biogeochemical activity - more intense than in 

adjacent habitats - affects the quality of water flowing through the interface. 

Hyporheic environments thus regulate water flow, and temporarily or 

permanently store organic, mineral and sometimes polluting matter. The 

microbial and animal components in them actively modify the timing and 

volume of nutrient and pollutant flows. From the structural viewpoint, the 

hyporheic zone is a matrix of permanently dark interstices saturated with 

water flowing slowly, with slight daily temperature variations and great 

bedrock stability. The hyporheic zone is an aphotic (without light), mechanical 

and biogeochemical filter between surface and underground water systems, 

ensuring their purification and maintenance. 

From this viewpoint, an important contribution came in 1993 from the 

American researchers Stanford and Ward with their concept of hyporheic 

corridor, which describes the connections and interactions between the 

hyporheic zone and the catchment basin. The role played by the hyporheic 

corridor in a catchment basin is essential for many ecological processes 

associated with nearby water sources: 1) the primary productivity in the 

Three-dimensional (longitudinal, transversal, vertical) nature of a river system 

stream above the hyporheic zone is strongly influenced by the distribution 

and frequency on the vertical scale of zones of upwelling (where the watertable 

supplies the stream), outwelling (areas where subsurface water supplies 

the stream laterally) and downwelling (areas where surface water supplies the 

water-table) of the stream, because the last two are usually richer in algal 

nutrients like nitrates and phosphates than surface water; 2) the temporal and 

spatial variability of processes of hydric exchange cause biodiversity in the 

hyporheic zone to increase more than in the adjacent water-table and surface 

habitats. 

Although Italian rivers are relatively well-known from the hydrological, 

biological and ecological viewpoints, an integrated overview of the Italian 

river ecosystem is still missing. Research emphasises a lateral dimension, 

i.e., the relationships between stream beds and surrounding floodplain and 

river areas in particular; a longitudinal dimension, i.e., the variations occurring 

along the length of rivers, from spring to outlet, although little is known about 

the vertical dimension, i.e., the relationships of rivers with their underlying 

aquifers. And the spatial scale is even less well-known in its temporal 

evolution. This three-dimensional spatial view, with the addition of a fourth 

temporal dimension, is the so-called four-dimensional nature of a river 

ecosystem (as defined by Ward). 

Spring at the base of a deposit of glacial origin (Pederù, South Tyrol) 

91

92 93 

The saline springs of Poiano: the importance of biological markers 

Fabio Stoch · Mauro Chiesi 

The Poiano Springs are the largest 

karstic springs in Emilia Romagna (mean 

discharge exceeding 400 l/s), and the 

main drainage system of groundwater 

flowing in the Triassic chalk of the Upper 

Val Secchia. Unlike other springs in the 

area, the Poiano Springs contain salt, 

with concentrations of dissolved sodium 

chloride between 5 and 7 g/l. Between 

autumn 2005 and spring 2007, the Trias 

Project (a research project by the 

Società Speleologica Italiana for the 

Ente Parco Nazionale dell’Appennino 

Tosco-Emiliano) was carried out on the 

Poiano aquifer, with automatic 

collection of the main environmental 

parameters (temperature, electric 

conductivity, pH, discharge) and 

continual collection of fauna by means 

of a net placed at the mouth of the 

spring. Geological and hydro-chemical 

tests showed that the chalk outcrops 

from which the springs gush are the top 

portion of a still active diapir, i.e., a 

chalk mass intruding vertically upwards 

because of its low density, bringing with 

it rock-salt, which makes the aquifer 

salty. Surface water, which infiltrates a 

few kilometres upstream through 

swallow holes, takes a few days to 

reach and mix with this salty water. This 

had led geologists to believe there was 

Nitocrella psammophila (left, 100 x), Niphargus poianoi (top, right, 6 x) and Pseudolimnocythere sp. 

(bottom, right, 100 x) 

a simple conduit system in the chalk 

bedrock, a typical feature of evaporites. 

The high content of sodium chloride is a 

limiting factor for biodiversity in the 

Poiano aquifer. Only three species of 

stygobiont crustaceans were collected 

from the springs: the harpacticoid 

Nitocrella psammophila and the ostracod 

Pseudolimnocythere sp., both of ancient 

marine origin, and the endemic 

amphipod Niphargus poianoi. However, 

contrary to previous ideas, biological 

research revealed that the conduit 

system does not carry to the springs the 

stygoxenic and stygobiotic organisms 

found in the streams flowing into swallow 

holes, none of which were collected in 

the Poiano Springs. Besides, the 

numbers of harpacticoids and ostracods 

coming from the springs are larger in 

periods of drought than in periods during 

which the aquifer is recharging, which 

suggested that the conduit system has a 

large groundwater basin. The integration 

of geological and biological research 

methods therefore enabled scientists to 

gain a better hydro-dynamic picture of 

the aquifer, and also revealed the 

unexpected presence of endemic 

species which had colonised the 

groundwater in the past and which are 

therefore now valuable bioindicators. 

Trends (measured during analysis) of discharge, precipitation and numbers of drifted stygobionts in 

the Poiano springs

94 ■ Ecology of springs 

95 

The perennial underground stream of the Pod Lanisce cave (Julian Pre-Alps, Friuli Venezia Giulia) 

Springs are like windows opening 

on the underground environment - 

Botosaneanu, a Romenian researcher, 

defined them as “the gates to the river 

Styx”. They are often the only means 

of analysing aquifers, because they are 

composed of surfacing groundwater 

which filters into recharge zones at 

different times, and reach spring 

points due to gravity. Springs may 

therefore be studied from the “outside” 

to analyse surface organisms 

colonising the crenal zone (thus, crenobiology), or from the “inside”, to 

examine the fauna of the aquifers supplying them - the stygian zone (thus, 

stygobiology). 

Springs are particular physical environments which have constant temperature 

over time and sometimes undergo changes in the chemical composition of their 

waters, due to the nature of the aquifers supplying them. These parameters 

define extreme natural situations. For instance, according to their thermic 

regime, there are thermal springs (like those in the Euganean Hills (Veneto), 

which host an endemic species of gastropods of the genus Heleobia) and 

glacial ones (such as those in the Adamello-Brenta, between Lombardy and 

Trentino, which are colonised by endemic stygophilic harpacticoid copepods). 

Brackish springs are saline (like the Poiano springs in Emilia Romagna, whose 

exclusive guest is the stygobiotic amphipod crustacean Niphargus poianoi), 

and those with particular values of pH and hydrogen sulphide, i.e., sulphuric 

springs, which are found throughout Italy and its islands. 

■ Groundwater inhabitants 

Sulphuric spring: the saline waters of Nirano 

(Emilia Romagna) 

The “darkness syndrome”. Contrary to ideas in the past, the underground 

environment can host great biodiversity. As described in the previous section, 

groundwater species may be divided into stygoxenes, stygophiles and 

stygobionts, according to their degree of dependency on this habitat for their 

survival. 

Stygobionts are species which are exclusive to groundwater and have 

developed special adaptations to life in this habitat. All their adaptations

96 

Modified sensory setae on the antennule of a male harpacticoid (top: ca. 2000x; bottom: ca. 4000x, 

photo by SEM, scanning electron microscopy) 

define the so-called “darkness 

syndrome”, a condition made up of a 

series of morphological, physiological 

and behavioural changes that these 

species underwent during their 

evolution in the geological past, which 

brought their ancestors from surface 

waters to the underground ecokingdom. 

According to how species 

react to the underground environment, 

adaptations are distinguished from 

Aesthetasc on antennule of a harpacticoid (ca. 

8000x, SEM photo) 

specialisations. Adaptations are strategies developed by species as 

responses to what are called the macrodescriptors of the underground 

environment, like constant darkness and scarce organic matter. Specialisation 

is the reaction to microdescriptors of the various types of habitats found in the 

hypogean environment in general. 

Groundwater organisms are depigmented (white, transparent or translucent), 

or sometimes pinkish (haematic pigments are visible through their semitransparent 

bodies), and their visual organs are generally small 

(microphthalmy) or totally absent (anophthalmy). Clearly, in totally dark 

environments, there is no advantage in having functioning visual organs or 

similarly, exhibiting gaudy colours. But it is more complex to understand what 

the disadvantages could be in maintaining these characteristics, since these 

same disadvantages often caused them to become extinct over time. 

Generally speaking, if an organism has a particular feature that is neither an 

advantage nor a disadvantage, a random neutral mutation may occur, causing 

that feature to disappear. In addition, if there is also an energy advantage, 

because during the ontogeny of these structures available energy can be used 

to develop compensatory sensory structures, then the loss of useless organs 

also has an adaptive logic. Presumably due to lack of resources, no stygobiont 

has developed the complex structures typical of animals living in sea abysses 

(like bio-luminescence). Moreover, pre-adaptive dynamics cannot be ruled 

out: in surface populations made up of both blind and sighted individuals, 

spatial segregation of blind phenotypes in groundwater and survival of sighted 

individuals in surface water may have given rise, over time, to two different, 

ecologically isolated genotypes. However, the evolutionary dynamics that led 

stygobionts to lose their eyes are still being discussed, as even within the 

same species eyes may show different evolutionary stages - for example, in 

some isopod, amphipod and decapod crustaceans. 

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98 

The lack of eyes or their functional atrophy is generally accompanied by 

hypertrophic (excessively developed) alternative sensory organs for life in a 

dark world, where smelling or touching the surrounding space is the only way 

of sensing the approach of predators or potential prey, finding a partner, or 

making one’s way in three-dimensional space, large or small. The body 

surfaces of stygobionts are therefore covered with sensory organs, which have 

different shapes according to species. For instance, crustaceans have 

aesthetascs, setae with many chemoreceptors sensitive to chemical stimuli, 

and thigmoreceptors, end-organs which respond to touch and enable 

organisms to find their way around by feeling the lake bed or single sand 

particles in interstitial environments. Stygobiont crustaceans living in free 

water sometimes have longer antennules than their surface relatives. These 

modified cephalic appendages are used to sense at distance: it is better to 

know in advance if a predator is coming, before it is too late to escape! In 

stygobionts, the compensatory length of sensory appendages is contrasted 

by clearly rudimentary locomotory appendages, which are much smaller than 

those of their close relatives living on the surface, and generally with fewer 

segments, setae and spines. This adaptation is actually a type of 

specialisation, as it is typical, or even exclusive, to interstitial species. 

The interstitial environment of hyporheic zones of rivers, springs and karstic 

springs covered by alluvial sediments has one great disadvantage: living 

Body elongation favours movement in the interstitial habitat 

spaces are restricted. In these narrow habitats, movement is confined, and 

walking species, let alone swimmers, are rare. Most of their time is spent 

moving around single sand particles, feeding on the bacterial biofilm covering 

the surface. Long legs would only hinder movement. This morphological 

adaptation is accompanied by a reduction in body size, as stygobiont species 

are generally smaller than their surface relatives. It is no coincidence that 

shorter legs and smaller bodies are often associated. The most probable 

reason is that these adaptations are the result of developmental heterochrony. 

Heterochrony. This is a deviation from 

the typical developmental sequence of 

formation of organs and parts as a 

factor in evolution, both in animals 

with discontinuous development (with 

larval stages separated by moults) 

and those with continuous, gradual 

transformations into adults. 

Although there are various types of 

heterochrony, the most commonly 

found in underground environments 

are progenetic paedomorphosis (also 

known as progenesis) and neoteny. 

Why has heterochrony been so 

successful in the colonisation of 

groundwater? 

Progenesis is the process by which 

Evolutionary dynamics of stygobiont progenesis 

features of the sexually mature animal 

develop precociously. The result of this deviation is a reproductively mature 

adult which preserves the morphological and/or physiological characteristics 

typical of juvenile or larval stages. These small adults often look like larvae 

and, if they are metameric (segmented) animals or have segmented body 

appendages, they may have fewer metameres and segments than they would 

if they had developed normally. But what is the advantage of being small? 

Obviously, it enables these animals to creep and wriggle into tiny interstitial 

spaces. Although heterochrony is the result of modifications - genome 

alterations which are generally disadaptive - it actually provides free admission 

to interstitial environments. It may therefore be a pre-adaptation, i.e., nonadaptive, 

and at times a neutral character or set of characters acquired in their 

original habitats (i.e., surface water) which may become useful when 

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100 

Theoretical evolutionary sequence which, starting from a large surface-living ancestor (1), through 

evolutionary steps (2-4), may have led to a progenetic interstitial species (5) 

organisms find themselves in new 

environments. Many of the 

evolutionary lines in stygobiotic 

crustaceans (copepods, ostracods, 

bathynellaceans, thermosbenaceans, 

asellid isopods, ingolfiellid and 

bogidiellid amphipods) originated in 

this way. 

Another type of heterochrony is 

neoteny. The final result is the same: 

sexually mature adults that look like 

larvae. In this case, the dynamics are 

different, because larval development 

is so slow that individuals reach 

sexual maturity without having 

completed their larval development. In 

this case, animals may grow to the 

same size or larger than their nonheterochronic 

relatives. The classic 

Elongation of the first antenna in the amphipod 

Hadzia fragilis stochi (ca. 8x) 

example of neoteny in underground environments is provided by the olm. 

Stygobiont animals also have physiological adaptations to life underground, 

like low metabolic rates and slow body growth, longevity, reduced fecundity, 

larger eggs richer in yolk (enabling embryos to survive for longer periods), and 

less frequent reproduction, often independent of the season and occurring 

throughout the year. 

However, like all generalisations, this too has its exceptions. For instance, in 

open karstic environments, some Niphargus species depend on the seasons. 

In particular, in spring, when aquifers increase their discharge due to 

snowmelt, and surface water carries larger amounts of organic matter, the 

biological cycle of these animals is timed in order to produce their juvenile 

stages which exploit the greater amount of food in order to develop. 

Other adaptive strategies. Another characteristic of all interstitial organisms 

is body elongation, which makes even phylogenetically distant taxa acquire a 

common worm-like shape (turbellarians, annelids, crustaceans and mites). 

The advantage is that their bodies are capable of wriggling into tiny interstices. 

Only a few ethological strategies for survival in particular underground 

environments are known. In hyporheic habitats, mainly in the upper layers of 

river sediments, where current velocity may be considerable, animals without 

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102 

Harpacticoid female of Morariopsis aff. 

scotenophila with only one egg per sac 

(ca. 100x) 

adhesive organs to cling to the 

sediments may curl around single 

particles, to prevent being carried 

away by the current. This is the case of 

oligochaetes, harpacticoid copepods 

and amphipods with elongated 

bodies. Others may become globose 

(some isopods and amphipods), and 

drift with the current to colonise new 

habitats. 

Another strategy adopted by 

crustaceans is gender segregation in 

spatial niches, to avoid intraspecific 

competition. When sampling a 

particular underground environment, 

scientists often collect larger numbers 

of males or, vice versa, of females. In 

addition to the sex ratio, which in 

nature is notably in favour of females, 

in interstitial environments, males and females may occupy microhabitats at 

different depths. Although little is known of the ethology of underground 

species, some male copepods occasionally re-clasp (mate with the same 

female) to ensure their paternity. 

Reproductive strategies. Until recently, the underground ecosystem was 

thought to be simple, stable and predictable. In fact, scientific research has 

proven this axiom invalid, at least for some habitats. 

Generally speaking, in physically predictable but ecologically unfavourable 

environments, species adopt a demographic strategy called A-selection 

(Adversity Selection), based on slow development and low fecundity in stressful 

environments with few resources and predictable changes. However, when 

habitats are still physically predictable and food resources are more abundant, 

species may turn to K-selection strategy, whereby populations grow to the 

carrying capacity of the environment. In this condition, intraspecies competition 

and predation may also become important for population dynamics. When 

environments are physically unpredictable but provide great food resources, 

there may be exponential population growth followed by plummeting figures 

when resources are no longer available: this is known as r-selection. Clearly, a 

single model cannot be applied to all underground species. 

■ The food-chain 

A classic description of underground environments is generally made by 

comparing its physical and biological organisations with those of surface 

environments. For example, groundwater is permanently dark and has no 

nyctemeral (day-night) cycle, whereas surface water is illuminated by the sun, 

and therefore does have a day-night cycle. This condition influences the 

biological and, equally importantly, the energy characteristics of the 

ecosystem. Lack of light results in detritus food-chains because there are no 

photosynthetic organisms (green plants) and very few chemo-autotrophic 

organisms (ones feeding on oxidised inorganic chemical compounds). These 

are bacteria that exploit chemical energy instead of light energy, and 

synthesise organic compounds from carbon dioxide. One of the typical 

locations is the Movile Cave (Romania), where these organisms are primary 

producers and the entire food-chain relies on them. There are also examples in 

Italian groundwater, an underground stream in the Grotte di Frasassi (Marches) 

and sulphuric basins in the Grotta del Fiume Sotterraneo in the Lepini 

mountains (Latium), which are still being studied. 

Therefore, with very few exceptions, the entire groundwater ecosystem is 

not self-sufficient, but depends on inputs of organic matter from terrestrial 

Sulphur spring in the cave of Cala Fetente (Capo Palinuro, Campania) 

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104 

Sketch showing degrading phases of particulate organic matter (POM) and its entry into the hyporheic 

environment (see text for abbrevations) 

and aquatic surface environments - defined by the French researcher Rouch 

as “epigean manna”. Due to the often total absence of primary producers, 

the aquatic underground environment is oligotrophic, i.e., deficient in 

nutrients and, as such, incapable of supporting long food-chains. There are 

only a few examples of dystrophic underground environments, which are 

periodically or occasionally filled with dissolved humic matter coming from 

the surface. 

Eutrophic conditions are associated with sudden increases in organic matter 

due to pollution. This happens in some saturated karstic habitats in periods of 

intense rainfall. Rain and surface organic matter percolate into aquifers 

through effective infiltration pathways, giving rise to large-scale although 

short-lived increases in organic matter available to biota. Similar events occur 

in unsaturated karstic environments, such as concretions and pools of 

trickling water in springs or hyporheic habitats, where the quantity of organic 

matter depends on the season. Clearly, the type of aquifer greatly affects the 

amounts of food available to underground communities, and may produce 

distinct community organisations. 

Most underground organisms are therefore detrivorous and feed on particles of 

organic matter produced by the decomposition of dead animal and plant 

organisms. This ingested matter is divided into two categories: Coarse 

Particulate Organic Matter (CPOM), with particles >1 mm, and Fine Particulate 

Organic Matter (FPOM), with particles 0.5 µm. Occasionally, some 

small organisms may feed on Dissolved Organic Matter (DOM) with particle 

sizes

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Hierarchical approach to the study of underground ecosystems: from large regional to small microhabitat 

scales 

Functional redundancy is a rare 

phenomenon in groundwater ecosystems, 

i.e., each trophic role is 

generally played by one or a few 

species, and there is little competition 

at each link of the food-chain. 

For the same reason, the ecosystem is 

certainly extremely vulnerable, as 

communities have low inertia (capacity 

for withstanding human disturbance 

unaltered). In fact, the extinction of one 

species of the community may bring 

the entire food-chain to a halt, with 

irreversible consequences for the 

whole ecosystem. Many underground 

species are therefore “key species”, as 

conservationist biologists call them. 

■ Stygodiversity: groundwater biodiversity 

Groundwater in a Tuscan cave 

Several factors contribute towards the spatial and temporal distributions of 

the so-called stygodiversity, and they may be both historical (palaeoclimatic, 

palaeogeographical and palaeoecological events) and ecological. The 

structure and functioning of underground aquatic ecosystems are the result of 

complex processes that may act in different ways at different spatial - and 

temporal - levels. These factors are therefore studied at continental or regional 

scale (mega- or macro-scale), aquifer (meso-scale) and microhabitat level 

(micro- or fine-scale). These scales are a series of spatial configurations fitting 

one into the other, and each level integrates the processes occurring at lower 

levels and is associated with others at the same level. This hierarchical 

subdivision into continental, regional, and sometimes aquifer levels allows us 

to focus on the palaeogeographical and palaeoclimatic events that influenced 

the origin of biodiversity in groundwater. 

The origin of stygobionts in fresh groundwater is double. Some of them evolved 

from ancestors living in continental surface freshwater (lakes and rivers) - most 

hydrobiid gastropods, cyclopoid copepods and many canthocamptid 

harpacticoids, asellid isopods, niphargid amphipods and olms - and are called 

limnicoid stygobionts. Others - polychaetes, parvidrilid oligochaetes, 

amphipods of the genera Hadzia and Salentinella, microcerberid, 

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108 109 

Stygodiversity in the Presciano springs: a pilot experiment 

Diana Maria Paola Galassi · Barbara Fiasca 

The Presciano springs make up one of 

the three great sources giving rise to the 

river Tirino in Abruzzi, at the foot of the 

greatest karstic aquifer in the 

Apennines. They have proved to be 

excellent natural laboratories for 

scientific research on the environmental 

factors affecting the spatial distribution 

of groundwater species (the spring area 

does not exceed 2000 m 2). 

This spring system is structurally 

complex, as a heterogeneous alluvial 

layer lies on strongly karstified bedrock, 

covering the underlying karstic aquifer. 

This situation has enabled researchers 

to examine how the different types of 

sediments affect the composition of 

underground communities. 

Detailed samplings have revealed that 

stygoxenic, stygophilic and stygobiont 

species are not at all homogenously 

distributed in the small spring area 

Presciano springs (Abruzzi) 

As depth increases, the relative 

importance of stygobionts increases to 

the detriment of other ecological 

categories, while stygophiles are 

generally found at intermediate depths 

(at 30 and 70 cm below the spring bed). 

This vertical distribution is a direct 

consequence of the ecological 

characteristics of stygobionts, which are 

morphologically and physiologically 

adapted to life in deep habitats, and of 

stygophiles, a transitional category that 

clearly prefers ecotonal areas. 

Stygoxenes are scattered, especially in 

subsurface sites, perhaps restricted by 

the low temperatures and oligotrophic 

conditions of the spring environment. 

Further analysis, carried out by 

dividing fauna living in karstic sites from 

that of alluvial sites, shows that 

stygophiles are almost exclusively 

found in the latter habitat. 

In addition, alluvial sites characterized 

by heterogeneous grain-size 

composition, with clearly alternating 

temporal upwelling and downwelling 

phases, host greater biodiversity, as 

they provide more ecological niches 

than karstic sites, and contain greater 

quantities of organic matter, which is 

trapped in interstices. 

Copepod taxocoenoses, the most 

important group in the analysed springs, 

are found in alluvial sites, with 15 out of 

the 17 species collected in the entire 

spring system. Instead, karstic sites 

host more monotonous karstic fauna, 

with one harpacticoid copepod 

(Nitocrella pescei) making up 90% of 

the entire assemblage. However, it is 

precisely in karstic sites that we find the 

most biogeographically interesting 

species, Pseudectinosoma reductum, a 

relict of ancient marine origin. 

Nitocrella pescei 

Distribution of ecological categories (number of 

specimens) at various depths (in cm)

110 

microparasellid and cirolanid isopods, ameirid and ectinosomatid harpacticoids 

and mysids - are related to taxa that are still living in marine environments and 

are called thalassoid stygobionts. The current distribution of stygobiont species 

is the result of an ever-changing mosaic of communities which have evolved on 

a geological time-scale and whose composition is still evolving. 

A particularly interesting aspect of the development of stygodiversity, which 

has long been debated by scientists, is the large number of relict species in 

underground communities. Some underground systems conserve species and 

even entire taxonomic groups related to now extinct ancient surface fauna (in 

one of his books, the French biologist René Jeannel spoke of cave-dwelling 

“living fossils”). Events like the Pleistocene glaciations, sea regressions and 

transgressions, and the salinity crisis of the Mediterranean have long been the 

focus of scientific debates on the origin of underground fauna. 

Some scientists believe stygobionts to be the “survivors” of surface 

populations which had taken refuge underground to escape harsh surface 

conditions (this “refugium” hypothesis goes back to the ideas of Charles 

Darwin). Others view colonisation as a continuous, ongoing process (the 

“active colonisation” hypothesis). 

Karstic spring (Friuli Venezia Giulia) 

According to the “refugium” theory, 

tropical regions, which were not 

affected by catastrophic events, would 

have scarce underground fauna; most 

importantly, surface populations, the 

ancestors of stygobionts, would 

generally have become extinct in 

geographical areas which underwent 

drastic climatic changes. 

Further knowledge has proved that 

both these theories were partly wrong, 

and suggested a new evolutionary 

scenario, according to which the 

present structure of stygodiversity has 

several causes. First, the extinction of 

surface populations is not a mandatory 

prerequisite for speciation in 

The endemic gastropod Bythiospeum calepii 

underground habitats. We already 

mentioned this when describing the coexistence of pigmented, eyed species 

of crustaceans with depigmented, anophthalmic or totally blind ones - many 

cases are known in Italy, especially for crustaceans of the genera Proasellus, 

Synurella and Gammarus. These are examples of ongoing active colonisation 

of groundwater not associated with dramatic changes in the surface 

environment. Stygobionts have also been found in all kinds of habitats in 

tropical areas - lava tubes on volcanic islands, cenotes in Mexico, caves in 

Somalia, anchialine systems in Australian deserts and in the caves of small 

islands in the Caribbean, and in Brazilian caves, inhabited by multitudes of 

blind fish - thus definitively contradicting the “refugium” hypothesis as the only 

explanation for the origin of underground communities. 

Although groundwater colonisation may occur independently of unfavourable 

conditions in the environments lying above, dramatic climatic and geological 

changes in surface habitats may in fact suddenly interrupt the genetic flow 

between hypogean and epigean populations. This explains the origin of 

“relicts”, both eco-geographical (separated from their closest surface relatives - 

still living and sometimes well diversified) and phyletic (the last survivors of a 

now extinct surface evolutionary line). 

Phyletic relicts are very interesting from the scientific viewpoint. Entire 

taxonomic groups (like bathynellaceans and thermosbaenaceans) belong to 

this category, and their closest relatives can no longer be found among the 

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animal groups still living on the surface. However, since the chronology of 

colonisation and speciation is hard to establish, a solution has been found in 

the so-called “molecular clocks”, which synchronise DNA mutations in living 

organisms with palaeogeographical and palaeoclimatic events. An example is 

afforded by the examination of Sardinian, Provençal and Tuscan species of 

stenasellid isopods, living evidence of the ancient tectonic fragmentation of 

the Tyrrhenian plate and drifting of the Sardinian-Corsican continental plate 

and its fragments from what is now Provence towards present-day Italy. 

Although necessary for speciation, vicariance (i.e., the splitting of the area of 

the old species into two parts separated by boundaries) is not only associated 

with these ancient, wide-ranging events, and may occur on any scale, from 

small, isolated fractures in karstic systems, to continents. Vicariant events may 

be geoclimatic and ecological: obviously, the efficiency of these “boundaries” 

is closely related to the ecology of the species, especially their aptitude for 

dispersal. Many stygobiont species are not prone to dispersal, and show 

Affinities between Provençal, Sardinian-Corsican and coastal Tyrrhenian fauna are explained by their 

common palaeogeographic history 

Niphargus similis, found in relict sites in glacialised areas of the Alpine chain 

limited geographic distribution (they are strict endemics). Furthermore, the low 

fecundity, benthic larval development and low dispersal potential of many 

interstitial crustaceans suggest that continuous and jump dispersal are quite 

rare in these groups. This is why stygobionts can be used as excellent 

historical (palaeogeographical) indicators, their descriptive capacity being 

similar to that of true fossils. 

Among the events that modelled present-day Italian stygofauna, the best 

known are certainly glaciations and sea regressions. The Quaternary 

glaciations depleted underground fauna in large areas of Italy, thus leading to 

the total absence of entire stygobiont genera of gastropods, copepods, 

isopods and amphipods north of the boundary of the Würmian glaciation. Sea 

regression, associated with glacial eustatism, trapped several taxa in coastal 

sediments, giving rise to stygobization. Very ancient regressive events led 

fauna of marine origin to become relicts, enigmatically confined and unevenly 

distributed in continental groundwater far from coastlines (amphi-Atlantic, 

Caribbean-Mediterranean, Caribbean-Mediterranean-Australian). In this case, 

the grandiose movements of plate tectonics were the main cause of 

relictualisation and, in the Mediterranean area, gave rise to the so-called 

Tethyan relicts, which date back to the disappearance of the ancient Tethys 

Sea in the Oligocene. 

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Despite its inhospitable appearance and lack of any ... - Udine Cultura

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