Macrobrachium sirindhorn Naiyanetr, 2001

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 : 638-641

Macrobrachium sirindhorn Naiyanetr, 2001

(figures 21, 22) Macrobrachium sirindhorn Naiyanetr, 2001: 609–616 , figures 1–2, pl.1 [type locality: Pong

Nam Dung waterfall, Mae Soon, Amphoe Fang, Chiang Mai Province, northern

Thailand].

Material examined

H: W, cl. 17.6 mm ( RMNH D 48632), Pong Nam Dung waterfall, Mae Soon, Fang, Chiang Mai, northern Thailand, coll. P. Naiyanetr, 23 April 1976 .

P: two WW, cl 12.5–14.5 mm ( ZRC 2000.2705 ), data same as holotype; 2 WW, cl 10.7–17.6 mm (CU1997.162), same data as holotype; 1 W, cl 16.2 mm (CU 1997.166), Ban Yang waterfall, Mae Ngon, Fang , Chiang Mai, 1 May 1977 ; 1 W, cl 14.0 mm, 1 X, cl 8.0 mm ( ZRC 2000.2696 ), Phu Sang Water, Chiang Kham , Phayao, 29 April 1976 .

Others. One specimen (CU 1997.164), Huai Chongkham, Muang, Mae Hong Son, 23 March 1979 ; 3 WW, cl 13.5–14.5 mm, 1 ovigerous X, cl 11 mm ( ZRC 2000.2706 ), Huai Khan, Muang , Mae Hong Son, 23 March 1979 ; 1 W, cl 16.2 mm (CU 1997.139), Fang, Chiang Mai, 23 March 1979; one specimen (CU 1997.163) , Ban Yang waterfall, Mae Ngon, Fang, Chiang Mai, coll. P. Naiyanetr, 24 April 1976; three specimens ( MNHN) , northern Thailand, coll. Pavie, no date.

Diagnosis

Rostrum short, straight or slightly convex, reaching to base of third segment of antennular peduncle or end of segment; rostral formula 3–4+5–7/2–3. Antennal and hepatic spines small. Eyes well developed, about 0.15 times as long as carapace. Scaphocerite 3.0 times as long as broad, with straight outer margin. First pereiopod with fingers as long as palm, chela 0.6 times as long as carpus. Male second pereiopods unequal. Major male second pereiopod distinctively longer than body, reaching beyond scaphocerite by half length of merus; covered with dense tufts of velvety setae along almost entire leg; fingers 0.5–0.7 times as long as palm, with 8–10 teeth on both cutting edges, not gaping with tips crossed when closed; palm laterally inflated, height 1.2 times as long as width, length 2.6 times as long as width; carpus short, conical, about half length of palm; merus slightly shorter than palm, greatly inflated. Minor male second pereiopod shorter than body, with fingers gaping when closed, entire leg covered with dense velvety setae as on major one. Third pereiopod reaching beyond scaphocerite by length of entire dactylus; dactylus 3.3 times as long as broad; propodus 6.0 times as long as broad, 2.6 times as long as dactylus. Uropodal diaeresis with a spine about half length of outer angle.

Remarks

Macrobrachium sirindhorn is most similar to M. pilosum Cai and Dai, 1999, but can easily be separated by the much stouter form of the second pereiopod, shorter fingers (0.5–0.7 times as long as palm versus slightly shorter than palm); the fingers with only 8–10 teeth on the cutting edge (versus 17); the more inflated palm (2.6 times as long as width versus 3.4 times); and most importantly, the strongly inflated merus (versus not inflated). The presence of the velvety setae on the inner margin of the merus can be used to easily separate M. sinrindhorn from other members of the M. pilimanus species group.