(Figs. 2A–D)

Material examined. 1 male, cl 3.70 mm, 2 ovigerous females, cl 4.40–4.50 mm (ZMB 29467), Papua New Guinea, Sadaun, Bewani Stn., stream at base of Bewani Mountains, 200–300m, 03°05.130’S 141°10.227’E; leg. M. Balke and K. Sagata, 12.IV.2006.

Diagnosis. Rostrum (Fig. 2A) straight, reaching to end of scaphocerite, 0.78–0.90 times as long as carapace, armed dorsally with 17 to 20 teeth including 2 or 3 on carapace posterior to orbital margin, terminal one-third of rostrum unarmed, 4 or 5 small ventral teeth. Pterygostomial angle broadly rounded. Antennular peduncle 0.70–0.83 times as long as carapace. Stylocerite 0.84–0.95 times as long as the basal segment of antennular peduncle. Carpus of first pereiopod (Fig. 2B) 1.45–1.54 times as long as wide, distally excavated; chela 1.81-1.96 times as long as wide; dactylus 1.08–1.26 times as long as palm; tips of fingers rounded. Merus of first pereiopod 1.3-1.5 times as long as ischium. Carpus of second pereiopod 3.37–3.91 times as long as wide, chela 2.08–2.29 times as long as wide, 0.88–0.91 times length of carpus; dactylus 1.25–1.39 times long as palm; tips of fingers rounded. Merus of second pereiopod 1.2–1.4 times as long as ischium. Dactylus of third pereiopod 3.50–3.64 times as long as wide (terminal spine included), terminating in 1 large claw and 5 or 6 spines on flexor margin; propodus 9.75–12.36 times long as wide, 3.86–4.25 times as long as dactylus. Fifth pereiopod slender, dactylus 4.0–5.2 times as long as wide (terminal spine included), with 1 large claw and 32-38 spines on flexor margin; propodus 10.33–11.43 times as long as wide, 3.65–4.00 long as dactylus. Epipods present on first 4 pereiopods. Endopod of male first pleopod (Fig. 2C) short, triangular, 1.4 times as long as proximal width, without appendix interna. Sixth abdominal segment 0.58–0.63 times length of carapace. Telson (Fig. 2D) 3.0 times as long as proximally wide, posterior margin rounded, without median projection, with 3 pairs of dorsal and 1 pair of dorsolateral spinules; distal end with 8–10 spines, lateral pair longer and stouter than intermediate spines. Preanal carina rounded, without a tooth or spine. Uropodal diaeresis with 12–13 movable spinules. Egg size of overigerous females 0.96–1.01 × 0.56–0.62 mm.

Distribution. Caridina demani is only known from some rivers in the northern part of New Guinea, especially from the rivers Tawarin (J. Roux 1911), Tami at Humboldt Bay, Tjano at Njao, Zoutbron (De Man 1915), Mamberamo (J. Roux 1927), and a stream at the base of Bewani Mt. (this study).

Remarks. Caridina demani is very similar to C. cognata De Man, 1915. It can be distinguished from C. cognata by the longer, distally unarmed rostrum and fewer teeth on the ventral margin (4 or 5 vs. 7–9 in C. cognata), by a stouter carpus and chela of the first and second pereiopods (carpus of first pereiopod 1.5, of second pereiopod 3.4–3.9 times as long as wide vs. 1.6–2.0 and 4.0–5.2 times as long in C. cognata). The specimens examined correspond well to the descriptions of J. Roux (1911, 1917, 1927) and De Man (1915). Only small differences were found in egg size (0.96–1.01 × 0.56–0.62 mm vs. 0.75–0.85 × 0.40–0.80 mm), which could be due to different developmental stages, different preservation state or method of measuring; and the length to width ratio of the carpus of the first (1.45–1.50 vs. 1.60–2.00) and second pereiopod (3.47– 3.91 vs. 4.0–5.0).

De Man (1915) described a high intraspecific variability in his material of C. demani. His specimens were larger than those examined by J. Roux (1911). They further showed a length to width ratio of the carpus (1.44–1.75 on the first and 3.33–4.00 on the second pereiopods and 6–9 ventral teeth on the rostrum). The measurements obtained from the three specimen in our collection fall into the range reported by De Man (1915). The differences between the type series of J. Roux (1911), the specimen reported from three different locations by De Man and our specimen should be regarded as intraspecific variation between populations from different habitats.