Pilocamptus schroederi

Pilocampus schroederi (van Douwe, 1915)

(Figs. 5–8)

Synonymy. Canthocamptus schroederi van Douwe, 1915: 263–265; Figs.1 View FIGURE 1 –7.

Material examined. 17 ovigerous females, 7 females, 15 males, one pair in copula; collected on 13 March 2014 in the pool next to the small spring near wall carving at Gonoa (Bardai region, northern Chad; 21o18'41'' N 16 o53'21'' E; altitude: 1068 m). One female and one male completely dissected, each of them mounted on one slide; access No.: PMSL-Copepoda-Brancelj-1359 (female), No.: PMSL-Copepoda-Brancelj-1360 (male); 10 ovigerous females, 3 females, one pair in copula, 7 males; stored in 70% alcohol; access No.: PMSL-Copepoda-Brancelj- 1361. The remaining material (7 ovigerous females, 3 females, 7 males) collected on the same date and the same location as previous material, deposited in the author’s collection.

Description. Female. Body length, measured from tip of rostrum to posterior margin of caudal rami, 548–622 µm (mean body length: 584 µm; n = 7); elongated, width evenly decreased from cephalothorax to last urosomite; preserved specimens colourless (Fig. 5A). Naupliar eye not discernible. Rostrum well developed, protruding forward at angle of 45o; rectangular with rounded free corners; about 2-times as long as wide; 2 sensilla close to tip (Figs. 5B, C).

Integumental window well visible, oval, with narrowing at 1/3 of its length. Cephalothorax smooth, prosomites, urosomites, and anal somite (incl. anal operculum); with several transversal rows of very fine spinules dorsally. Posterior margins of prosomites and urosomites finely serrated dorsally (Figs. 5A, G). Genital doublesomite with row of robust spinules at distal margin laterally (Figs. 5A, D, E). Genital complex with single large copulatory pore, sclerotized, copulatory duct bell-shaped. Seminal receptacles small, simple, heavily sclerotized. P6 reduced, represented by fused plate well above seminal receptacles; with one long seta on each side of plate (Fig. 5E).

Row of robust spinules on third urosomite laterally and ventrolaterally; short gap between spinules ventrally; fourth urosomite with continuous row of robust spinules laterally and ventrally, unequal in length; anal somite with short row of robust spinules laterally (Figs. 5A, D).

Anal operculum medium-sized, not overreaching distal end of anal somite; with straight free margin, row of small spinules along it (Figs. 5A, F, G).

Caudal rami slightly conical, diverging, slightly curved; each ramus about twice as long as wide, with weak keel dorsally (Figs. 5A, D, F). Distal half of caudal ramus with oblique row of 6–7 robust spinules, positioned from outer lateral side to ventral side of ramus (Figs. 5F, G). Anterolateral external accessory seta (I) very short, thin; positioned next to seta (II). Anterolateral external seta (II) as long as width of ramus, inserted at 1/4 of its length. Posterolateral seta (III) positioned close to ventral side of ramus, at about 2/3 of its length. Outer apical seta (IV) spiniform, smooth, as long as caudal ramus. Inner apical seta (V) long, spiniform, with row of small spines on both sides after breaking plane; basal part swollen into hump-like form, with bright dorsal surface. Inner accessory seta (VI) spiniform, as long as seta II, smooth. Dorsal seta (VII) slightly longer than width of caudal ramus; inserted on internal side of it, at about 1/3 of its length.

Antennule (Figs. 5A, 6A) 8-segmented. Aesthetasc on segment 4 cylindrical, with rounded tip; reaching well above tip of segment 8. Second aesthetasc on apical segment about half of length of first one, cylindrical. Both aesthetascs as acrotheck (common base of seta and aesthetasc; ae). Setal formula: 1.8.5.2+ae.1.2.1.6+ae.

Antenna ( Fig. 6 View FIGURE 6 B) with allobasis and robust, 1-segmented Exp and Enp. Allobasis with 2 setae; one short, smooth, near the base; one longer, unipinnate, at about 1/2 of its length. 2 strong spines on outer (anterior) margin of Enp, increasing in length distally; one robust spiniform seta on inner (caudal) margin. Apical armature with one robust inner spine and 4 soft setae; 3 of them geniculate. Exp with 4 spiniform, unipinnate setae; 2 apically, 2 laterally; subequal in length.

Labrum ( Fig. 6 View FIGURE 6 C) with 2 spiniform setae on outer margins, unequal in length; a row of fine setules apically.

Mandible ( Fig. 6 View FIGURE 6 D) short, robust; with 3 strongly chitinised teeth on gnathobase. Dorsal seta near gnathobase. Mandibular palp 2-segmented, each segment about as long as wide; distal segment with 3 smooth setae, increasing in length. Group of fine spines and groups of short setules near mandibular palp.

Maxillule ( Fig. 6 View FIGURE 6 E) with strong, robust spines on praecoxal arthrite. Innermost spine with rounded tip. Spiniform, smooth seta dorsally. Coxa with one strong, chitinised spine with rounded tip and one slim seta. Basis with weak beak-like outgrowth with few spines distally; long smooth seta, slightly longer than beak-like outgrowth. Exp and Enp reduced, with one and 2 smooth setae, respectively.

Maxilla ( Fig. 6 View FIGURE 6 F) 2-segmented; syncoxa with 2 endites with 3 and 2 elements, respectively. Basis drawn in strong beak-like spine with few distal spinules; Exp and Enp reduced to 4 setae.

Maxilliped ( Fig. 6 View FIGURE 6 G) comprising syncoxa, basis and 1-segmented Enp. Syncoxa with seta on distal corner. Basis 2-times as long as wide, with 8–10 spinules near palmar margin dorsally, increasing in length distally. Enp drawn out into strong, acutely curved claw; as long as basis, armed with several spinules in distal half; additional armature represented by a short seta.

P1 with 3-segmented Exp and Enp; P2–P4 with 3-segmented Exp and 2-segmented Enp. Exps with rows of strong spinules on lateral and distal margins of segments. Armature formula of P1–P4 as in Table 4.

Leg Coxa Basis Exopod Endopod

1 2 3 1 2 3 P 1 0-0 1-I 0-I 1-I 0-2+I-I 1-0 1-0 0-2+I P 2 0-0 0-I 0- I 1-I 1-1 +I-III 0-0 2-2+I - P 3 0-0 0-I 0- I 1-I 2-1 +I-III 0-0 2-2+I - P 4 0-0 0-I 0- I 1-I 2-1 +I-III 0-0 2-1+I - Enp of P1 slightly longer than Exp (Fig. 7A). Basis with long, slim spiniform seta on inner margin; stout basal spine on outer margin. Exp-1 with strong outer spine; Exp-2 with one strong external spine and one short, slim and smooth seta on inner distal corner. Exp-3, with one spine subapically, one spine with blunt tip and 2 geniculate setae apically; outer about 2/3 of inner length. Enp-1 with one strong spiniform seta on inner margin. Enp-2 with one slim, smooth seta at distal inner corner. Enp-3 with one spine and one long geniculate seta apically; one soft, smooth seta on inner margin, slightly longer than outer spine.

P2 (Fig. 7B) basis with one spiniform seta on outer margin. Enp almost as long as Exp-1 and Exp-2 combined. Exp-1 as long as wide, with one strong spine at 2/3 of outer margin length. Exp-2 with one strong spine on outer margin; one short, robust seta at distal inner corner. Exp-3 3.5-times as long as wide, with 3 spines along outer margin; 2 elements apically: 1 spiniform seta with spinules unilaterally, one long seta, as long as Exp-3. Inner margin with one long, unilaterally feather-like seta at 1/2 of segment length. Enp-1 short, with no armature. Enp-2 3.5-times as long as wide, with 2 short, robust setae along inner margin at 1/3 and 2/3 of segment length. 3 elements apically: 2 long soft setae, subequal in length; one robust spiniform outer seta, shorter than Enp-2.

P3 (Fig. 7C) with one long, thin seta on outer margin of basis. Enp as long as Exp-1 and Exp-2 combined. Exp- 1 and Exp-2 similar to that of P2. Exp-3 3.5-times as long as wide; 3 long spines along outer margin; one relatively weak, long spine apically. Inner margin with one short seta at 1/2 of margin length and one long seta subapically, as long as Exp. Enp-1 and Enp-2 as in P2; Enp-2 about 4-times as long as wide.

P4 (Fig. 7D) Exp similar to that of P3, with less robust armature. Enp-1 small, about half as long as wide, with no armature. Enp-2 with one outer spine and one long seta apically; one slightly shorter seta on inner margin subapically. Additional one long seta at 1/2 of inner margin length.

P5 (Fig. 7E) not fused. Exp and baseoendopod distinctly separated; baseoendopodal lobe well developed, longer that Exp; with 5 elements on endopodal part; one soft, smooth seta on outer margin of basis. Outermost 2 short bipinnate spines unequal in length; one seta apically, about 3-times as long as outer spines. Inner seta subapically; about 0.8 length of apical one, soft; innermost element bipinnate spine, as long as second outer spine. Exp lobe slightly longer than wide, with one short smooth spine at 1/2 of outer margin length; one long, thin outer spine apically; one long, thin inner seta; on inner margin one short spine subapically. Hyaline field not well developed.

P6 (Fig. 5E) fused, small, forming simple plate; each with one thin long seta.

Egg sac with 8- 12 eggs.

Male. Body length, measured from tip of rostrum to posterior margin of caudal rami, 471–500 µm; average: 487 µm (n = 4); elongated, widest at distal part of cephalothorax, the rest of the body slightly narrower; evenly tapering toward anal segment; preserved specimens colourless ( Figs. 8 View FIGURE 8 A, B). Naupliar eye not discernible. Rostrum well developed; as in female. Integumental window not discernible. Cephalothorax smooth; prosomites, urosomites, anal somite with several transversal rows of very fine spinules dorsally. Posterior margins of thoracic and abdominal somites dorsally finely serrated ( Fig. 8 View FIGURE 8 A). First urosomite with no ventral spinules. Second, third and fourth urosomites with row of robust spinules laterally and ventrally. Anal somite with 2 strong spinules ventrally, at the inner corner of the base of furcal ramus; unequal in length ( Fig. 8 View FIGURE 8 B). Anal operculum well developed, only slightly rounded, not overreaching distal end of anal somite, with about 20 fine spinules along distal margin ( Fig. 8 View FIGURE 8 A).

Caudal ramus conical, slightly longer than wide, inner and outer margin slightly convex; weak dorsal keel; rami slightly diverging ( Figs. 8 View FIGURE 8 A, B). Anterolateral external accessory seta (I) slightly longer than caudal ramus, smooth; anterolateral external seta (II) shorter than seta I, smooth; positioned at the 2/3 of caudal ramus length. Posterolateral seta (III) very short, spiniform. Outer apical seta (IV) spiniform, as long as caudal ramus, unipinnate; no fracture plane. Inner apical seta (V) very long, but shorter than urosome, robust, with strong spinules on distal half; no fracture plane. Inner accessory (VI) very short. Dorsal seta (VII) as long as caudal ramus, inserted medially, at about 1/2 of its length.

Antennule ( Fig. 8 View FIGURE 8 C) haplocerate, robust, 7-segmented, strongly chitinised. Geniculated articulation between fifth and sixth segment. Aesthetasc on fifth segment cylindrical, extending over distal segment; aesthetasc on seventh segment half of length of previous one. Setal formula: 0.7.5.2.5.1.7.

Antenna, mandible, maxillule, maxilla, maxilliped, P1 similar to those in female.

P2 ( Fig. 8 View FIGURE 8 D): Exp similar to those in female. Enp 2 segmented. Enp as long as Exp-1 and Exp-2 combined. Enp-1 0.75-times as long as wide, with no seta on inner distal corner. Enp-2 3-times as long as wide, with setae along inner margin at 1/3 and 2/3 of segment length; 2 soft setae apically, equal in length, about twice as long as segment bearing them; outer margin with several strong spinules.

P3 ( Fig. 8 View FIGURE 8 E): Exp similar to that in female. Enp 3-segmented, as long as Exp-1 and Exp-2 combined. Enp-1 half as long as wide, with no armature. Enp-2 with long apophysis with spear-like tip; reaching distal margin of Exp-3. Enp-3 about 3-times as long as wide, with 2 relatively long setae apically.

P4 ( Fig. 8 View FIGURE 8 F): 3-segmented Exp and 2-segmented Enp. Enp expanding over middle of Exp-2. Exp in armature similar to female’s but less robust; with feather-like inner seta subapically. Enp-1 half as wide as long, with small inner seta. Enp-2 with one blunt outer spine apically, as long as segment bearing it; one soft inner seta, twice as long as spine. One blunt spine along inner margin subapically, about 1.5-times as long as outer spine.

P5 ( Fig. 8 View FIGURE 8 B) fused. Exp and baseoendopod well separated; baseoendopod well developed, with strong bipinnate spine. Exp longer than baseoendopod, slightly longer as wide, with 4 elements: one outermost seta spiniform, accompanied by short spinule; next to it one short seta, about 4-times as long as outermost spiniform seta; one long seta apically, about twice as long as outer soft seta; inner margin with one robust spine with few long setules unilaterally, spine as long as Exp.

FIGURE 5. Pilocamptus schroederi (van Douve, 1915), female: A, habitus, dorsal view; B, rostrum, frontal view; C, rostrum, lateral view; D, urosome, ventral view; E, genital double-somite; F, anal somite and furcal rami, dorsal view; G, 4th urosomal and anal somite with furcal ramus, lateral view

FIGURE 7. Pilocamptus schroederi (van Douve, 1915), female: A, P1; B, P2; C, P3; D, P4, E, P5.

P6 ( Fig. 8 View FIGURE 8 B) fused, small, forming simple plate; with no armature.

Variability. Minor variation in the number of spinules on abdominal somites and legs in both sexes. Remarks. The genus Pilocamptus contains fourteen species according to Wells (2007), Pesce (2014) and the World Register of Marine Species (WoRMS) by Gaviria-Melo & Walter (2014) ( Table 5 View TABLE 5 ) but 13 according to Defaye & Dussart (2011), who considered P. georgevitchi (Chappuis, 1923) a synonym of P. p i l os u s. The genus covers a wide geographical area (either sensu WoRMS register or Pesce/Wells), spanning from central Europe ( P. pilosus and P. georgevitchi ) to sub-Saharan Africa and Madagascar, inhabiting predominantly surface water bodies ( Table 5 View TABLE 5 ).

Genus: Pilocamptus Distribution *Incl.: P. k. kamerunensis (Kiefer, 1928) and P. k. villosus (Chappuis, 1932)

+ Questionable species (after Pesce 2014); # synonym of P. pilosus (after Defaye & Dussart 2011)

Specimens collected from the far north of the Chad fit the description of P. schroederi which was provided by van Douwe as Canthocamptus schröderi (see van Douwe 1915). That description was based on three females collected from Lake Victoria/Nyanza (Mwanza?). A male was described one year later by Menzel (1916), who collected a sample containing seven females and one male from wet moss (in about 1 ml of water) from “East Africa”. Both authors mentioned the half-ball shaped base of the inner terminal (V) seta, well visible from a lateral view, and also an oblique row of short, robust spines along the distal outer margin of the furcal ramus in the female. Both characters are also well visible in specimens recently collected from Chad. The most evident difference between specimens from Lake Victoria and the spring in Chad is the much more elongated segments on P1–P4 of females from the lake (van Douwe 1915). There are also some differences in body length of females between specimens described by van Douwe (1915) (0.8 mm) and Menzel (1916) (0.5 mm), while specimens from Chad range from 0.548 to 0.622 mm, which is an intermediate position.

The location from Chad provides the third known locality of the species. Unfortunately Menzel (1916) did not give a more detailed location of his material than “East Africa”. So far, three samples have been collected in different habitats. In East Africa specimens were collected from the littoral zone of a lake (van Douwe 1915) and from wet moss beds ( Menzel 1916) while, in Chad, they were found in a small spring in the Sahara. The listed locations are about 3000 km apart, almost in a north–south direction and with contrasting climates. The location in Chad is isolated on the northern slopes of an ancient volcano at an elevation of about 1070 m where there is no additional surface water. The population depends on the small amount of seepage water fed from an aquifer in porous material.

The minor differences in ornamentation and their similar body sizes support the idea that populations have not been in contact since the Holocene wet climate interval (i.e. about 6000 years ago; Kröpelin et al. 2008).