Macrobrachium amplimanus Cai and Dai, 1999

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 : 637-638

Macrobrachium amplimanus Cai and Dai, 1999

Macrobrachium amplimanus Cai and Dai, 1999: 231 , figures 14–16 [type locality: Xishuangbanna , Yunnan, China].

Material examined

H: W, cl 14 mm ( IZAS), forest stream near Mengla County, coll. J. Li and Y. Wei, 20 March 1983.

P: One W, cl 12.5 mm ( ZRC 2000.2737 ), same data as holotype .

North Thailand. Fifteen WW, cl 9.5–13.5 mm, 2 XX, cl 10.7–13.2 mm, 2 ovigerous XX, cl 10.3–13.8, eggs 1.6× 1.2 mm ( ZRC 2000.2692 ), roadside market from Nan to Chiang Mai, coll. Y. Cai, 11 June 1998 ; 4 WW, cl 12.7–15.23 mm (CU 1997.133), Chiang Mai, 5 May 1972 ; 5 WW, cl 13.3–17.5 mm, 1 ovigerous X, cl 11.5 mm (CU 1997), Chiang Mai, 22 February 1992; seven specimens (CU 1997.132) , Chiang Mai, 22 February 1992 .

North-east Thailand. Two WW, 9.2–11.7 mm, 3 XX, cl 7.8–10.0 mm ( ZRC 2000.2691 ), Loei Province, Mekong basin, Nam Huang, rapids at Bau Keng Tou, 17°42∞2◊N, 101°24∞24◊E, coll. M. Kottelat and K. Kubota, 31 January 1999 .

West Thailand. Six WW, cl 8.0– 12.6 mm, 4 XX (one ovigerous, eggs 1.5× 0.95 mm), cl 8.5–9.0 mm (CU1997.129), Kanchanaburi, no date.

South Thailand. One W, cl 13.5 mm ( ZRC 2000.2690 ), Narathiwat province, hill stream in plantation at end of road branching west at about km 7 on road from Waeng to Ban Bu Ke Ta, 5°52∞6.6◊N, 101°49∞47.1◊E, pH 6.8, coll. M. Kottelat, 2 November 1995 .

Diagnosis

Rostrum short, straight, reaching to or slightly beyond base of third segment of antennular peduncle, not reaching middle of this segment; rostral formula 3–4+6–8/2–4. Male second pereiopod unequal. Major male second pereiopod slightly longer than body, reaching beyond scaphocerite by one-third length of merus; covered with dense tufts of velvety pubescence on almost entire chela; fingers subequal to palm, with 11–15 teeth on both cutting edges, not gaping when closed, tips crossed; palm laterally inflated, height 1.3 times as long as width; carpus short, conical, about half length of palm; merus slightly shorter than palm, greatly inflated, 2.1 times as long as wide, 2.4 times as long as high. Third pereiopod propodus 2.6 times as long as dactylus. Eggs 0.95–1.20× 1.5–1.6 mm in diameter.

Remarks

The short, stout and inflated second pereiopods easily distinguishes M. amplimanus from the rest of the M. pilimanus species group. Even females of M. amplimanus have stout, inflated second pereiopods, as in males. Macrobrachium amplimanus differs from M. pilimanus by the form of the rostrum, the postorbital teeth being more widely spaced than the anterior dorsal rostral teeth and occupying one-third the length of the carapace (versus postorbital teeth more closely spaced than the anterior dorsal rostral ones and occupying 0.14–0.20 times the length of the carapace), the prominent preanal carina (versus indistinct), the trilobed epistome (versus bilobed, see figure 16A in Cai and Dai, 1999 versus figure 16C in present paper); the more pointed processes on the first three abdominal sternites (figure 14B in Cai and Dai, 1999 versus figure 16D in present paper), and the propodus of the third pereiopod being 2.5 times as long as the dactylus (versus 3.2 times). Macrobrachium amplimanus can be separated from M. hirsutimanus by the trilobed epistome (versus bilobed, figure 15B); and the less prominent processes on the first three abdominal sternites. Macrobrachium amplimanus can be distinguished from M. eriocheirum by the propodus of the third pereiopod being 2.6 times as long as dactylus (versus 3.3 times); the shorter fingers of the second pereiopod (shorter than palm versus subequal to palm in M. eriocheirum ) and the more inflated palm (1.6 times as long as wide versus 2.0 times in M. eriocheirum ). Macrobrachium amplimanus can be differentiated from M. forcipatum by the relatively shorter rostrum (not reaching beyond middle of third segment of antennular peduncle versus reaches beyond), the pointed process on the third abdominal sternite (versus absence of process); and the shorter fingers of second pereiopod (shorter than palm versus subequal to palm).