Caridina cognata De Man, 1915

Karge, Andreas, Rintelen, Kristina Von & Klotz, Werner, 2010, On two small collections of freshwater shrimps (Decapoda: Atyidae: Caridina) from Papua New Guinea, with descriptions of two new species *, Zootaxa 2372 (1), pp. 138-150 : 141-142

Caridina cognata De Man, 1915

( Figs. 2E–H )

Material examined. 1 male, cl 4.0 mm, 4 ovigerous females (eggs without eyes), cl 4.80–5.00 mm ( ZMB 29468), Papua New Guinea, East Sepik, Prince Alexander Mountains, Wewak , 400m, 03°37.319’S, 143°36.764’E; leg. M. Balke, 21.IV.2006 .

Diagnosis. Rostrum ( Fig. 2E ) straight, triangular in lateral view, reaching near to or slightly beyond end of antennular peduncle, 0.65–0.81 times as long as carapace, armed dorsally with 21–27 teeth, including 2 or 3 on carapace posterior to orbital margin, 7–9 ventral teeth. Armature of rostum reaching to tip of rostrum on dorsal margin, ventral margin toothless near the tip. Pterygostomial angle subrectangular. Antennular peduncle 0.60–0.83 times as long as carapace. Stylocerite 0.83–0.95 times as long as basal segment of antennular peduncle. Carpus of first pereiopod ( Fig. 2F ) 1.61–1.95 times long as wide; chela 1.82–2.05 times as long as wide; dactylus 0.93–1.30 times as long as palm; tips of fingers rounded. Carpus of second pereiopod 4.00–5.18 times as long as wide, chela 2.27–2.61 times as long as wide, 0.79–0.84 times length of carpus; dactylus 1.21–1.50 times long as palm; tips of fingers rounded. Dactylus of third pereiopod 3.08–4.20 times as long as wide (terminal spine included), terminating in one large claw, with 5 spines on flexor margin; propodus 9.18–11.69 times long as wide, 3.71–4.16 times as long as dactylus. Fifth pereiopod slender, dactylus 4.0–5.4 times as long as wide (terminal spine included), with one large claw and 44 or 45 spines on flexor margin; propodus 10.63–13.57 times as long as wide, 3.37–3.52 long as dactylus. Epipods present on first 4 pereiopods. Endopod of male first pleopod ( Fig. 2G ) short and triangular, without appendix interna. Sixth abdominal segment 0.54–0.59 times length of carapace. Telson ( Fig. 2H ) 3.2–3.5 times as long as proximally wide, with very small or without median projection, with 3–5 pairs of dorsal and one pair of dorsolateral spinules; distal margin convex with 7 or 8 spines, lateral pair longer than intermediate spines. Preanal carina rounded, without a tooth or spine. Uropodal diaeresis with 9–13 movable spinules. Egg size of ovigerous females (eggs without eyes) 0.96–1.03 × 0.58–0.65 mm.

Distribution. Caridina cognata is only known from some rivers in the northern part of New Guinea.

Remarks. According to De Man (1915), C. cognata is very similar to C. fecunda J. Roux, 1911 from Western New Guinea and C. aruensis J. Roux, 1911 from Aru Island. Caridina cognata can be distinguished from C. fecunda by the well developed epipods (mastigobranchs) on the first four pereiopods (vs. epipods only on pereiopods 1–3 in C. fecunda ). Caridina aruensis is a species belonging to the C. nilotica species group, its taxonomic status having been previously discussed ( Johnson 1963 as C. simoni aruensis ; Chace 1997 as C. nilotica typica ). According to the original description of C. simoni Bouvier, 1904 and the discussion in Cai & Wowor (2007) on C. sarasinorum Schenkel, 1902 , the distal portion of the dorsal margin of the rostrum is unarmed in this species and is thus not a member of the C. nilotica species group. Regardless of the systematic status of C. aruensis , the rostrum of C. cognata is armed throughout its dorsal margin, and lacks a separate subapical tooth; and thus can be easily distinguished from C. aruensis or species of the C. nilotica group. Caridina cognata is also morphologically similar to C. novaecaledoniae J. Roux, 1926 from New Caledonia, but differs from this species by its relatively longer rostrum (reaching to or beyond distal end of the antennular peduncle vs. never reaching to in C. novaecaledoniae ) and a higher number of teeth on the dorsal margin (21–27 vs. 12–22 in C. novaecaledoniae ). Furthermore, the fingers of the first chelipeds seem to be proportionately longer in relation to the palm in C. cognata (dactylus 0.93–1.30 times as long as palm vs. slightly shorter or as long as palm in C. novaecaledoniae ), according to the original description (J. Roux 1926, p. 215, fig. 53).

De Man (1915) reported C. cognata and C. demani from the same locality. In his descriptions he did not compare both species, although they share some characters. They differ only in the length, shape and armature of the rostrum as well as in the proportions of the first two pereiopods. However, De Man indicated a high intraspecific variability in both species also depending on the age of the specimens. In the present material, we only found minor differences with De Man’s original description of C. cognata , i.e. slightly stouter carpi of the first pereiopods (1.61–1.95 times as long as wide vs. 1.8–2.5 times) which we regard as intraspecific variation.

Figures

FIGURE 2. Caridina demani, male (cl 3.7 mm) (ZMB 29467): A, cephalothorax; B, first pereiopod; C, endopod of male first pleopod; D, distal end of telson. Caridina cognata male (cl 4.0 mm) (ZMB 29468): E, cephalothorax; F, first pereiopod; G, endopod of male first pleopod; H, distal end of telson. Scale bars = 2.0 mm (A, E), 1 mm (B, D, F, H) or 0.5 mm (C, G).