Research Article |
Corresponding author: John D. Taylor ( j.taylor@nhm.ac.uk ) Academic editor: Graham Oliver
© 2019 John D. Taylor, Emily A. Glover.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Taylor JD, Glover EA (2019) Unloved, paraphyletic or misplaced: new genera and species of small to minute lucinid bivalves and their relationships (Bivalvia, Lucinidae). ZooKeys 899: 109-140. https://doi.org/10.3897/zookeys.899.47070
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Species identified as Pillucina are paraphyletic in molecular analyses and a new generic name, Rugalucina, is introduced for a complex of three similar species Rugalucina angela from the northern Indian Ocean and Red Sea, R. vietnamica from South East Asia, and R. munda from northern and north eastern Australia. Lucina concinna from the Red Sea, previously synonymised with P. vietnamica/angela is recognised as a Rugalucina-like species but with a very short anterior adductor scar. Divaricella cypselis from Karachi is similarly now recognised as a distinct species, probably related to Rugalucina but with oblique commarginal sculpture and a short adductor scar. A group of minute Indo-West Pacific lucinids with highly unusual multi-cuspate lateral teeth and previously classified as Pillucina are separated under a new genus Pusillolucina gen. nov., with the description of three new species P. arabica, P. africana, and P. biritika from the Arabian Gulf, Mozambique, and Madagascar. Finally, a new genus, Notocina, is introduced for the small southern Atlantic species, Epicodakia falklandica, shown in molecular analyses to be misplaced at subfamily level and now classified in Lucininae and not Codakiinae with Epicodakia.
bivalves, chemosymbiosis, taxonomy, Indo-West Pacific, South Atlantic
Within the chemosymbiotic bivalve family Lucinidae, genera in the Loripes group have been identified as monophyletic (
The other lucinid separated by paraphyly and not closely related to the other Pillucina species is the minute Pillucina pusilla from the Philippines that possesses distinctive multi-cuspate lateral teeth. This extremely unusual character was first recognised in Pillucina denticula Glover & Taylor, 2001 from near Durban, South Africa. Recently, we have identified herein other species of minute lucinids with similar dentition from the Arabian Gulf, Mozambique and northern and southern Madagascar. Species with this dentition form a morphologically distinct clade that we recognise with a new generic name.
Additionally, amongst these small lucinids it is apparent that the southern Atlantic species Epicodakia falklandica Dell, 1964 is misclassified because molecular results (
During the last 20 years there has been a marked proliferation of generic categories within Lucinidae building on and revising the prior classifications of
IWP Indo-West Pacific
L shell length
LV left valve
P1 protoconch 1 length
P2 protoconch 2 length
RV right valve
SEM scanning electron microscopy
sh complete shell both valves
v single valve
Lucina (Codakia) angela Melvill, 1899. Here designated.
Small L to 15 mm, sub-circular, sculpture of fine, commarginal lamellae crossed by strong radial ribs more prominent to anterior and posterior, with overall crinkled appearance, ligament largely internal, obliquely inset, anterior adductor muscle scar ventrally detached from pallial line for half of length, inner shell margin crenulate.
From Latin ruga for wrinkle or crease and Lucina, feminine.
Lucina (Codakia) angela Melvill, 1899, Pillucina vietnamica Zorina, 1978, Lucina (Codakia) munda A. Adams, 1856. Tentatively included: Divaricella cypselis Melvill, 1918 and Lucina concinna H. Adams, 1871.
Rugalucina is part of the broader Loripes group within the Lucininae, all having an obliquely inset internal ligament. Other genera within the group are Pillucina, Pusillolucina Wallucina, Lucinella, Chavania, and Keletistes. Of these only Pillucina, Pusillolucina, and Rugalucina have prominent radial sculpture. In shell characters Rugalucina differs from Pillucina in the more strongly divergent radial sculpture, the longer anterior adductor muscle scar and the more coarsely crenulate inner shell margin.
In molecular analyses members of the Loripes group form a monophyletic subclade of Lucininae. Seven species of putative Pillucina have been included in analyses (
Previously, we regarded Pillucina vietnamica as a wide-ranging species in the northern Indian Ocean through south east Asia to southern China (
Lucina concinna H. Adams, 1871 previously placed in the synonymy of P. vietnamica by
Single gene tree for the Loripes group of genera and species based on cytochrome b gene sequences, using Bayesian inference as implemented by MrBayes. Support values are posterior probabilities. Methods as in
Lucina fischeriana Issel, 1869: 83–84, pl. 1, fig. 8 (non L. fischeriana d’Orbigny, 1845: Jurassic fossil).
Lucina (Codakia) angela Melvill, 1899: 98, pl. 2, fig. 8.
Loripes fischeriana:
Pillucina fischeriana:
Pillucina fischeriana:
Pillucina angela:
Pillucina vietnamica
(part):
Pillucina angela:
Pillucina angela
(part):
Lucina fischeriana 5 syntypes (
L. angela two syntypes NHMUK1899.12.18.20-21; L 7.9 mm and 6.1 mm; 1 syntype
Gwadur, Pakistan, 8 fathoms (15 m).
Small (L to 15 mm), subcircular, inflated. Colour white, yellow or orange. Waxy appearance. Sculpture of strong diverging radial ribs, broader and more widely spaced to the anterior and posterior. Ribs crossed by fine, closely spaced, commarginal lamellae which curve over ribs producing a roughly scabrous appearance. Central parts of shell generally without ribs. Lunule large, broadly lanceolate, smooth. Ligament internal, obliquely inset. Hinge: RV with single large cardinal tooth and short anterior and posterior lateral teeth, LV with two cardinal teeth, lateral teeth consisting of small sockets. Anterior adductor scar narrow, elongate, detached from pallial line for ca. half of length. Pallial line irregularly lobate, or slightly divided. Inner shell margin coarsely crenulate to anterior and posterior.
Red Sea: Great Bitter Lake (Hoffman et al. 2006), Suez Canal, El Ballah (
Rugalucina angela (as Pillucina vietnamica) is recorded as an invasive species off Israel in the eastern Mediterranean (
Rugalucina angela shows variation in shell morphology between various localities around the Arabian Peninsula and Red Sea. For example, shells from the Arabian Gulf are usually smaller, while those from the northern Red Sea as on Gulf of Suez shores are generally larger, and the marginal crenulations stronger. We regard these differences as ecophenotypic probably associated with the extreme environmental conditions such as the very high salinities experienced in the southern Arabian Gulf, usually more than 40 psu but in shallow lagoons as high as 52–55 psu (
Rugalucina angela is closely similar in shell morphology to R. vietnamica and R. munda. The differences are subtle; externally they share diverging radial ribs that are stronger to anterior and posterior, and the fine commarginal lamellae. Rugalucina angela has a shorter anterior dorsal area, larger hinge plate and teeth, and a slightly more divergent anterior adductor scar. Rugalucina vietnamica is higher, with a longer anterior dorsal area. Rugalucina munda is similar but the radial sculpture is much less pronounced with finer margin denticulations and subdued commarginal sculpture.
Rugalucina angela (Melvill, 1899). A–C Syntype of Lucina (Codakia) angela Melvill, 1899 (
Pillucina vietnamica Zorina, 1978:195, figs 3 & 6).
Pillucina vietnamica:
Pillucina vietnamica
(part):
Pillucina vietnamica:
Pillucina angela
(Melvill, 1899) (part):
Pillucina vietnamica syntypes (
Intertidal, south coast of Hainan, China.
Small (L to 10 mm), sub-circular, longer than high, posteriorly slightly truncate, moderately inflated. Shell white, slightly translucent and waxy in appearance. Sculpture of many, fine, low, commarginal lamellae and low radial ribs which are broader and more prominent towards the anterior and posterior. Radial ribs are conspicuously fluted where commarginal lamellae cross giving a crinkled appearance. Lunule elongate, lanceolate and impressed, slightly asymmetrical. Ligament internal, short, situated on a broadly triangular resilifer. Hinge: right valve with single, cardinal tooth, anterior and posterior lateral teeth small, posterior tooth elongate. Left valve with two narrow cardinal teeth, a small anterior lateral socket and posterior lateral narrow socket. Anterior adductor muscle scar medium-long, detached for ca. 50 % of length. Posterior scar ovate. Pallial line entire, sometimes partially discontinuous or irregularly lobate. Shell margin crenulate, with crenulations coarser towards anterior and posterior.
Singapore: Pulau Semakau (
Intertidal to shallow sub-tidal seagrass and muddy habitats. Recorded at high densities in muddy seagrass and mangrove fringe habitats of eastern and western Thailand (
Although we formerly recorded Rugalucina vietnamica with a broad longitudinal range from the northern Red Sea to southern China (
Rugalucina vietnamica (Zorina, 1978). A–C Pillucina vietnamica Zorina, 1978 syntypes (
Lucina (Codakia) munda A. Adams, 1856: 225 not figured.
Syntypes
: 3 whole shells
Moreton Bay, Queensland, Australia.
Australia: Western Australia: Parry Harbour, Kimberley (
Small, L to 11 mm, sub-circular, posteriorly slightly truncate in juveniles, shallow posterior sulcus, moderately inflated. Shell colour white, internally often yellowish. Sculpture of fine, low commarginal lamellae crossed by low radial ribs which are broader and more prominent towards the anterior and posterior. Radial ribs are slightly fluted where crossed by commarginal lamellae. Lunule elongate, lanceolate, slightly asymmetrical. Ligament internal, short, situated on a broadly triangular resilifer. Hinge: right valve with single, narrow, cardinal tooth, anterior and posterior lateral teeth small; left valve with two narrow cardinal teeth, small anterior lateral and posterior lateral teeth. Anterior adductor muscle scar medium length, detached for ca. 50 % of length. Posterior scar ovate. Pallial line entire, irregularly lobate. Shell margin finely crenulate, with crenulations coarser towards anterior and posterior.
Northern and north eastern Australia.
Intertidal and shallow subtidal muddy sand, nearshore seagrass and mangrove fringe.
Rugalucina munda
is closely similar in shell morphology to R. vietnamica and R. angela and we previously confounded the species (
Rugalucina munda (
Here we include two species from the northern Indian Ocean and Red Sea that are similar externally to Rugalucina vietnamica but differ from it and each other in shell sculpture, hinge, and muscle scar characters. No molecular material is available for firmer placement of either species.
Divaricella cypselis Melvill, 1918: 156, pl. 5, fig. 33.
D. cypselis holotype
Karachi, Pakistan, 20–30 fathoms (36–55 m).
Pakistan: Karachi, Winckworth collection (
Small (L to 5.2 mm), sub-circular, inflated. Colour white or yellowish. Sculpture of diverging, curved, radial ribs prominent to anterior and posterior but are subdued or absent in middle parts of shell. Ribs crossed by closely spaced, narrow, low, commarginal lamellae that are aligned obliquely to the ventral shell margin (Fig.
Known from the northern Arabian Sea and southern India. Probably more abundant in the northern Indian Ocean but unrecognised.
The obliquely inset internal ligament indicates placement in the Loripes group of genera and while the external sculpture resembles Rugalucina in radial ribbing the obliquely aligned commarginal lamellae are similar to that seen in Lucinella divaricata (Linnaeus, 1758) from the eastern Atlantic but that species lacks any radial ribbing.
‘Rugalucina’ cypselis (Melvill, 1918). A–D Holotype Divaricella cypselis Melvill, 1918 (
Lucina concinna H. Adams, 1871: 791, pl. 48, fig. 13 (non Lucina concinna Deshayes, 1857 an Eocene fossil).
Loripes concinnus:
? Pillucina concinna:
Pillucina cypselis
(Melvill, 1918):
Pillucina vietnamica:
Holotype of Lucina concinna
cracentis Latin, genitive singular of cracens meaning neat, graceful. Adjective.
Ovoid shape, slightly higher than long, diverging radial ribs, ligament short, largely internal, hinge with ventral flexure, right valve with single large cardinal tooth, anterior adductor muscle scar short.
Small, L to 9 mm. ovoid, slightly higher than long (H/L 1.01), inflated, umbones prominent, rounded. Colour white or yellowish. Sculpture of diverging radial ribs, coarser and more widely spaced to anterior and posterior, ribs finer and more subdued in middle parts of shell. Ribs crossed by fine, low, closely spaced, commarginal lamellae. Lunule short, heart shaped. Ligament short, obliquely inset. Hinge line with ventral flexure (Fig.
Red Sea: Egypt: Gulf of Suez (ZMC), Port Safaga (Dekker colln), Ras Baghdadi (Dekker colln), Sharm el Naga (Dekker colln), Makadi Bay (Dekker colln), Gulf of Aqaba: Dahab (Blatterer colln), Yemen -al Durayhimi (Dekker colln), Aden (
The ovoid shape and flexured hinge line with the large cardinal tooth in the right valve are features of Pillucina s. s. but Pillucina species usually have less prominent radial ribbing (
‘Rugalucina’ cracentis sp. nov. A–E Lucina concinna Holotype (ZMC I.100470) Gulf of Suez, exterior and interior of right and left valves and dorsal view, L 9.2 mm F–H ‘Rugalucina cracentis’ exterior of right valve and interior of right and left valves Egypt, Dahab, Gulf of Aqaba, Red Sea. H. Blatterer colln, L 6.7 mm I, J R. cracentis exterior and interior of right valve Dahab, Gulf of Aqaba, Red Sea, H. Blatterer colln, L 8.5 mm K, L R cracentis exterior and interior of left valve Egypt, 4 km north of Port Safaga, H. Dekker colln 6930, L 8.3 mm M interior of right valve, L 8.8 mm N, O exterior and interior left valve Egypt, 4 km north of Port Safaga, H. Dekker colln 6930, L 7.1 mm P, Q interiors of right and left valves, H. Dekker colln 6930, L 8.7 mm R, S hinge details of P and Q.
Pillucina pusilla Glover & Taylor, 2016. Here designated. Philippines.
Very small, L to 3 mm, sub-circular, higher than long. Umbones prominent. Sculpture of thin commarginal lamellae, elevated to anterior and posterior, crossed by radial ribs that are more prominent to anterior and posterior. Lunule broadly lanceolate, concave. Ligament short, largely internal. Hinge: RV with single cardinal tooth, large anterior lateral tooth and a complex multi-cuspate posterior lateral tooth consisting of up to ten cusps; LV with two cardinal teeth, the anterior larger, posterior lateral tooth formed of sockets for projecting cusps of the right valve. Anterior adductor scar very short, barely detached from pallial line, pallial line irregularly discontinuous. Inner shell margin crenulate.
Derived from Latin pusilla meaning very small and Lucina. Feminine
Pusillolucina is similar in many external characters including shape and sculpture to some Pillucina (type species Pillucina spaldingi Pilsbry, 1921 = Pillucina hawaiiensis (Smith, 1885)). By comparison no Pillucina species possess the unusual multi-cuspate posterior dentition. Moreover, Pusillolucina pusilla is distinct in molecular analyses (Fig.
Pillucina pusilla, Pillucina denticula Glover & Taylor, 2001, Pusillolucina africana sp. nov., Pusillolucina arabica sp. nov., Pusillolucina biritika sp. nov. These species differ mainly in characters of the dentition.
Indo-West Pacific, low intertidal to 70 m.
Pillucina pusilla
Holotype
:
Philippines, Bohol Island, Manga, 9°41.1'N, 123°51.4'E, 3–4 m, mud, [PANGLAO 2004: stn S19].
Very small, glossy, L to 1.8 mm, sub-circular, higher than long, inflated. Umbones prominent. Sulci and dorsal areas poorly defined. Sculpture of thin commarginal lamellae elevated to anterior and posterior, with 17–25 low, rounded radial ribs, divaricate in anterior part of shell. Juvenile shell with elevated commarginal lamellae but no radial ribs. Microsculpture of fine growth increments only. Protoconch P1 +P 2 = 134 µm, P2 with numerous growth increments. Lunule broadly lanceolate, depressed, asymmetric, larger part in left valve. Ligament short, internal, oriented parallel to cardinal teeth. Hinge: right valve with single cardinal tooth, large anterior lateral tooth and posterior lateral tooth consisting of four or five cusps, left valve with two cardinal teeth, the anterior larger, anterior lateral socket, posterior lateral with sockets for cusps of the right valve. Anterior adductor scar very short, barely detached from pallial line, pallial line irregularly discontinuous. Inner shell margin coarsely crenulate.
Pusillolucina pusilla and P. denticula. A–D Pusillolucina pusilla (Glover & Taylor, 2016) A Pillucina pusilla Holotype (
Pillucina denticula Glover & Taylor, 2001: 271, figs 7a–g.
Holotype
:
Durban Bay, South Africa.
Shells small, L to 3.5 mm, robust, sub-circular to ovoid in outline. Sculpture of fine, closely spaced, commarginal lamellae crossed by low, rounded radial ribs that are prominent and broader towards anterior and posterior. Ribs inconspicuous in central part of shell. Lunule long, lanceolate. Ligament internal, short. Right valve with a single cardinal tooth, a prominent anterior lateral tooth and a long posterior lateral tooth divided into 8–10 small cusps. Left valve with two cardinal teeth, a small anterior lateral and a posterior tooth divided into sockets for cusps of the RV. Anterior adductor muscle scar short and barely detached from the pallial line. Inner shell margin crenulate, with crenulations more widely spaced anteriorly.
Holotype
:
Arabian Gulf, Tarut Bay, Saudi Arabia, dredged (17.5.1971) K. Smythe collection.
arabica from Latin arabicus. Used as an adjective.
Pusillolucina with posterior lateral teeth divided into four or five cusps and sockets.
Shell very small, L to 2.4 mm, ovate, umbones prominent, sculpture of closely spaced, narrow, commarginal lamellae, sometimes elevated at posterior and anterior dorsal margins, crossed at anterior and posterior by low radial ribs, juvenile shells with commarginal lamellae only. Colour: white, translucent when wet. Protoconch: P1 84 µm, P1 + P2 = 155 µm, P2 with numerous growth increments. Lunule broadly lanceolate, smooth. Ligament internal, short, set alongside cardinal teeth. Hinge: right valve with single cardinal tooth, anterior lateral tooth located above anterior adductor muscle. Posterior lateral tooth long, divided into four or five cusps, left valve with two cardinal teeth, the anterior larger, anterior lateral tooth small, posterior lateral tooth divided into four or five sockets for cusps of right valve. Anterior adductor muscle scar short, barely detached from pallial line, posterior scar ovoid. Inner shell margin crenulate, more strongly to anterior and posterior.
Pusillolucina arabica differs from the Philippine P. pusilla by the more ovate outline, and the less prominent commarginal and radial sculpture. By comparison, P. africana has finer more closely spaced commarginal sculpture and more cusps (7–8) on the posterior lateral tooth. From South Africa P. denticula has much finer commarginal sculpture and up to 10 smaller cusps on the posterior lateral tooth. From Madagascar P. biritika sp. nov. has only three cusps on the posterior lateral tooth.
Despite its small size, P. arabica has the characteristic, thick inner ctenidial demibranchs with a well-developed bacteriocyte zone packed with symbiotic bacteria ca 3–4 µm (Fig.
Pusillolucina arabica sp. nov. Tarut Bay, Saudi Arabia, Arabian Gulf. A–C Holotype (
Pusillolucina arabica sp. nov. Arabian Gulf
Holotype
:
Mozambique, Inhaca Island, Baia Campessuane, 3–4 m, INHACA stn MD1, 26°03.6'S, 32°56.6'E. 25NOV2011.
Named for Africa, used as an adjective.
Pusillolucina with posterior lateral teeth divided into seven or eight cusps and sockets.
Shell very small, L to 2.4 mm, ovate, umbones prominent, sculpture of closely spaced, narrow, commarginal lamellae, sometimes slightly elevated at posterior and anterior dorsal margins, crossed at anterior and posterior by low radial ribs, juvenile shells with commarginal lamellae only. Protoconch: P1 ca 75 µm, P1 + P2 = 140 µm, P2 with numerous growth increments. Lunule long, broadly lanceolate, smooth. Ligament internal, short, set on triangular resilifer alongside cardinal teeth. Hinge: right valve with single cardinal tooth, anterior lateral tooth located above anterior adductor muscle. Posterior lateral tooth long, divided into seven or eight cusps, left valve with two cardinal teeth, the anterior larger, anterior lateral tooth small, posterior lateral tooth with seven or eight sockets for cusps of right valve. Anterior adductor muscle scar short, barely detached from pallial line, posterior scar ovoid. Pallial line continuous. Inner shell margin crenulate, more strongly to anterior.
For comparison with other species see P. arabica above.
Pusillolucina africana sp. nov. Mozambique, Inhaca Island, Baia Campessuane, 3–4 m, INHACA stn MD1. B–O Paratypes (
Holotype
:
Holotype
: South Madagascar east of Cap Antsirabe, 49–52 m, ATIMO-VATAE stn TP11, 25°02.8'S, 47°01.3'E. 06MAY2010 (
Paratypes
: South Madagascar east of Cap Antsirabe, 49–52 m, ATIMO-VATAE stn TP11, 25°02.8'S, 47°01.3'E. 06MAY2010 (
South Madagascar off Baie Fort-Dauphin 54–56 m, ATIMO-VATAE stn TP18, 25°02.4'S, 47°03.2.6'E, 11MAY2010 (
Northwest Madagascar, S of Cap St Sébastien, 42–44 m, MIRIKY stn DW3202, 12°35.6'S, 48°49.9'E, 29JUN2009 (
Biritika, meaning extremely small in Malagasy. Used as a noun in apposition.
Pusillolucina with posterior lateral teeth divided into three cusps and sockets.
Very small, L 1.5 mm, sub-ovate, longer than high, umbones prominent. Sculpture of fine commarginal lamellae crossed at anterior and posterior by low, rounded, radial ribs, juvenile shells with commarginal lamellae only. Some lamellae extended as scales along posterior dorsal margin. Lunule long, lanceolate. Ligament short internal on short resilifer. Hinge: RV with single cardinal tooth and single anterior lateral tooth, posterior lateral tooth short, divided into three cusps, LV with two cardinal teeth the posterior-most thin, posterior lateral tooth with three sockets for cusps of the right valve. Anterior adductor muscle scar short, barely detached from pallial line, posterior scar ovate. Pallial line entire. Shell margin coarsely crenulate, more strongly to anterior and posterior.
Pusillolucina biritika sp. nov. A, B South Madagascar east of Cap Antsirabe, 49–52 m, ATIMO-VATAE stn TP11, 25°02.8'S, 47°01.3'E. (
Epicodakia falklandica Dell, 1964. Here designated.
Small (L to 3 mm), sub-ovoid, slightly longer than high. Umbones prominent. Posterior dorsal margin straight. Sculpture of low, rounded, commarginal lamellae with poorly defined fine radial ribs to anterior and posterior. Microsculpture densely punctate. Ligament short, protrudes above dorsal margin. Lunule broadly lanceolate. Hinge line narrow, left valve with two small cardinal teeth and anterior and posterior lateral teeth. Right valve with single, slightly bifid cardinal tooth and anterior and posterior lateral teeth. Anterior adductor muscle scar short, slightly detached from pallial line, inner shell margin finely denticulate.
notos in Greek meaning south, -cina as an abbreviation of Lucina. In reference to the southern Atlantic distribution. Female gender.
Epicodakia falklandica Dell, 1964: 206, fig. 4 (17, 18, 19).
Holotype
:
Off Falkland Islands, Discovery station WS 766. 44°58'S, 60°05'30"W, 545 m. Paratype depth range 105–219 m.
South Georgia, 53.561108S, 37.88494W, 221 m BIOPEARL cruise 1, 05.04.2006 sample B-06-1167. GenBank numbers: 18S KF741615, 28S KF741644, cyt b KF741675.
Shells small, L 2–3 mm, ovoid, slightly longer than high. Umbones prominent. Posterior dorsal margin straight. Sculpture of low rounded commarginal lamellae with narrow interspaces. Faint radial ribs visible to anterior and posterior. Microsculpture of dense fine punctae (2–3 µm in diameter). Protoconch: P1 = 188 µm, P1 + P2 = 242 µm, P2 with fine growth increments (South Georgia shell). Ligament short, protruding above posterior dorsal margin (Fig.
South Atlantic: around Falkland Islands (
Notocina falklandica (Dell, 1964). A–D Holotype of Epicodakia falklandica (
There is a general perception that bivalves having chemosymbiosis with thiotrophic or methanotrophic bacteria are large, as exemplified by Vesicomyidae (Calyptogena magnifica Boss & Turner, 1980, 263 mm), Modiolinae (Bathymodiolus boomerang Cosel amp; Olu, 1998, 360 mm), Solemyidae (Acharax bartschi (Dall, 1908), 210 mm) that live at hydrothermal vents and hydrocarbon seeps. Among the several bivalve families with chemosymbiotic life habits Lucinidae is by far the most diverse with more than 400 species occupying a wide range of habitats from the intertidal to bathyal depths and spanning a wide size range from 1.5 to 170 mm. The largest living species are Meganodontia acetabulum Bouchet & Cosel, 2004 with shell lengths up to 170 mm and Codakia distinguenda (Tryon, 1872) at 160 mm, while the Eocene fossil, Superlucina megameris (Dall, 1901), attained a shell height of 310 mm (
One of the foci of this paper has been the recognition of some very small lucinid species within the new genus Pusillolucina with adult shell lengths of 1–3 mm. All the species in this genus have a very unusual multi-cuspate lateral dentition not seen in any other lucinids. The recognition of these minute lucinids extends the morphological and functional range of Lucinidae. Even the smallest have chemosymbiosis with thickened ctenidial demibranchs occupied by symbiotic bacteria. Other minute lucinids include Guyanella clenchi (Altena, 1968) 1–2 mm and Parvilucina latens Taylor & Glover, 2016, 2–3 mm, both documented from Guadeloupe but likely occur more widely in the western Atlantic (
Another small species that has been phylogenetically misplaced is Notocina falklandica widely recorded from outer shelf and bathyal depths around the Falkland Islands, Argentina and Uruguay. Since the original description by
Two species described here, Rugalucina angela and ‘R.’ cracentis, are abundant in the northern Red Sea where a surprising number of other lucinids have been recorded. From intensive sampling around Safaga Bay (
Special thanks are due to Suzanne Williams (
We are grateful to colleagues at the
Finally, we thank two reviewers and the editors of ZooKeys for helpful suggestions.