Macrobrachium sp.

Cai, Y., Naiyanetr, P. & Ng, P. K. L., 2004, The freshwater prawns of the genus Macrobrachium Bate, 1868, of Thailand (Crustacea: Decapoda: Palaemonidae), Journal of Natural History 38 (5), pp. 581-649 : 641-643

Macrobrachium sp.

(figure 23)

Material examined

One X, cl 16 mm (CU 1997.166), Fang, Chiang Mai, northern Thailand, coll. P. Naiyanetr, 1 May 1977 .

Diagnosis

Rostrum (figures 23A, B) slightly downturned, reaching to end of antennular peduncle or end of segment; rostral formula 3+7/2. Antennal sharp, situated at inferior orbital angle; hepatic spines small, lying behind and below antennal spine. Eyes well developed, 0.15 times as long as carapace. Telson (figure 23D) 2.1 times as long as wide, with two pairs of small dorsal spines, ending in a median point, lateral spines small, smaller than dorsal spines, intermediate spines well developed, with long plumose setae at distal margin. Epistome (figure 23C) trilobed by two shallow grooves. Basal segment of antennular peduncle distinctly longer than both second and third segments. Scaphocerite (figure 23E) 2.5 times as long as broad, with straight outer margin. First pereiopod (figure 23F) reaching beyond end of scaphocerite by half of carpus, with fingers slightly shorter than palm, chela 0.7 times as long as carpus. Second pereiopod distinctively shorter than body, reaching beyond scaphocerite by carpus; smooth, merus 2.5 times as long broad; carpus conical, cup-shaped, 1.7 times as long as high; chela with fingers 0.6 times as long as palm, no denticles on cutting edges; palm 2.5 times as long as broad. Third pereiopod reaching beyond end of scaphocerite by length of entire dactylus; propodus 7.0 times as long as broad, 3.0 times as long as dactylus. Uropodal diaeresis with a spine about half length of outer angle.

Remarks

With regards to the form of the rostrum and second pereiopod, the present specimen is close to M. amplimanus except for the surface of the leg, which is glabrous while that of M. amplimanus is covered by velvety pubescence, and the cutting edges on the fingers of the second pereiopod are unarmed (versus with teeth). We are unable to assign this single female specimen with certainty to any of the known Macrobrachium species and it seems to belong to an undescribed taxon. The lack of a male specimen, which would show more characters, prevents us from formally naming it for the time being.