Macrobrachium forcipatum Ng, 1995

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 : 630-633

Macrobrachium forcipatum Ng, 1995

(figures 18E, F, 19)

Macrobrachium forcipatum Ng, 1995: 249 , figures 2–4 [type locality: Tasek Temengor , northern peninsular Malaysia].

Materials examined

H: W, cl 14.1 mm ( ZRC 1995.264 ), Tasik Temengor, south of Banding , Sungai Halong, coll. K. K. P. Lim and H. H. Tan, 1–4 November 1993 .

P: 12 WW, 2 ovigerous XX, cl 8.6–10.4 mm, eggs 1.7× 1.1 mm ( ZRC 1995.265 ), data same as holotype .

South Thailand. Twelve WW, cl 10.0–14.0 mm, 8 XX, cl 8.5–11.5 mm, 6 ovigerous XX, cl 8.2–9.2 mm, egg with eyes, 1.2×1.0 mm ( ZRC 2000.2643 ), Narathiwat Province, Ban Sac tributary of Sungai Kolok, ca 19.5 km westwards towards Waeng at T-junction from Sungai Kolok to Waeng and Sungai Padi , 5°47.49∞N, 101°80∞E, pH 7.6, coll H. H. Tan et al., 23 October 1998 ; 12 WW, cl 7.5–13 mm, 3 XX, cl 7.5–12 mm, 16 ovigerous XX, cl 8–12 mm ( ZRC 2000.2703 ), Nam Tok Tone Sai , Phuket, coll. P. K. L. Ng and H. H. Tan, 8 April 1998 ; 12 WW, cl 12–14 mm, 3 ovigerous XX, cl 9–11 mm ( ZRC 2000.2675 ), Nam Tok Ton Sai , Phuket; 7°55.96∞N, 98°19.43∞E, coll. P. K. L. Ng and H. H. Tan, 8 April 1999 ; 3 WW, cl 11.1–15.3 mm (CU 1997.135), Satun, coll. P. Naiyanetr, 22 March 1982 ; 3 WW, cl 9.8–16.5 mm, 3 XX, cl 7.5–8.0 mm, 8 ovigerous XX, cl 8.5–10.5 mm, eggs with eye spot, 1.5× 1.2 mm ( ZRC 2000.2672 ), Narathiwat Province, Nam Tok Sipo , downstream area, 6°16.06∞N, 101°38.65∞E, coll. H. H. Tan et al., 24 October 1998 ; 6 WW, cl 9.7–11.4 mm, 4 XX, cl 8.5–9.2 mm, 10 ovigerous XX, cl 8.5–11.5 mm, eggs 1.4×1.0 mm ( ZRC 2000.2671 ), Songkhla Province, Nam Tok Khao Chong km 25 on road to Trang from Phattalung, 7°39.71∞N, 100°2.33∞E, coll. H. H. Tan et al., 26 October 1998 ; 16 WW, cl 10.0– 12.6 mm, 5 ovigerous XX, cl 8.2–9.6 mm, 46 specimens ( ZRC 2000.2674 ), Songkhla Province, Plak Khlong, Padi fields on road to Thale Noi from Phatalung , 7°44.46∞N, 100°4.83∞E, coll. H. H. Tan et al., 25 October 1998 ; 1 W, cl 13.5 mm, 1 ovigerous X, cl 8.0 mm, eggs 1.5×1.0 mm ( ZRC 2000.2676 ), Satun Province, stream in Ban Kong Kruat , pH 6.0, coll. M. Kottelat, 4 November 1995 ; nine specimens (5 ovigerous XX), Narathiwat Province, stream at Phu Khao Tong, 6 km west of Ban Buke Ta , pH 6.5, coll. M. Kottelat, 2 November 1995 ; 2 WW, cl 7.8–11.6 mm, 1 X, cl 8.5 mm, 1 ovigerous X, cl 10.0 mm, eggs with eyes, 0.8× 1.4 mm ( ZRC 2000.2673 ), Narathiwat Province, Bocha Bhudo Padee National Park , 6°29.99∞N, 101°38.15∞E, pH 7.2, coll. H. H. Tan et al., 24 October 1998 ; 1 W, cl 12.0 mm, 3 ovigerous XX, cl 9.5–11.0 mm ( ZRC 2000.2681 ), Sungai Kolok , coll. K. Kobota, no date; 3 WW, four other specimens, Phuket, 18 March 1982 ; 1 W, cl 13.0 mm (CU 1997.138), Kakhon, Si Thammarat, 19 May 1976 , coll. P. Naiyanetr; 1 W, cl 13.1 mm (CU 1997.127), Krabi, 28 October 1988 ; 1 W, cl 9.0 mm, 1 ovigerous X, cl 9.0 mm, seven other specimens (CU 1997.17), Bang Pat waterfall, Phuket, 9 August 1986 ; 20 specimens (CU 1997.18), Kathu waterfall, Phuket, 17 October 1986 ; 1 W, cl 8.0 mm, 1 ovigerous X, Thai Muang, Phang Nga, 25 August 1986 ; 15 specimens, cl 9.0–11.0 mm (CU 1997.22), Phang Nga, 1 April 1986 ; 1 W, cl 12.5 mm, 1 ovigerous XX, cl 9.0 mm, Thap Put river , 24 August 1986 ; four specimens (CU 1997.85), Phang Nga, 7 September 1986 ; 3 WW (CU 1997.124), Phang Nga, 16 March 1989 ; 1 W (CU 1997.152), Satun, coll. P. Naiyanetr, 22 March 1982 ; five specimens, Uttaradit, 20 February 1997 ; five specimens (CU 1997.157), Phang Nga, coll. P. Naiyanetr, 17 March 1982 ; 3 WW, cl 13.2–13.4 mm (CU 1997.136), Songkhla, 22 March 1982 ; 5 WW, cl 12.5–14.45 mm (CU 1997.130), Songkhla, 22 May 1982 ; 2 WW, cl 13.3–12.5, 1 X, cl 11.9 mm (CU 1997.124), Phang Nga, 16 March 1989 ; 2 WW, cl 11.2–11.3 mm, 1 ovigerous X, eggs 1.3×1.0 mm (CU 1997.151), coll. Sari Chumphon, 12 December 1981 ; 1 W, cl 12.7 mm (CU 1997.125), Pattani, coll. S. Panha, 25 March 1982 ; 2 XX, cl 8.2–11.0 mm (one ovigerous, eggs with eye spots, 1.6× 1.3 mm) (CU 1997.128), Nakhon Si Thammarat, 19 May 1976 ; 2 WW, cl 11.2–13.0 mm (CU 1997.145), Nakhon Si Thammarat, coll. P. Naiyanetr, 9 March 1976 ; 2 WW, cl 13.0– 14.5 mm (CU 1997.154), Sarat Thani, 27 March 1982 ; 6 WW, cl 9.5–14.0 mm, 2 ovigerous XX, cl 0.85 mm (CU 1997.1), Phang Nga, coll. P. Naiyanetr, 1989; 2 WW, cl 11.5–12.5 mm, 3 ovigerous XX, cl 8.0– 8.5 mm (CU 1997.2), Ramun waterfall, 2 km from Phang Nga, 9 August 1982 ; 6 WW, cl 10.0– 12.5 mm, 1 ovigerous X, cl 10.0 mm (CU 1997.3), Tao Thong waterfall, Thap Put Phang Nga, 8 March 1986 ; 3 WW, cl 7.8–9.5 mm, 2 XX, cl 7.2–8.0 mm (CU 1997.4), Takua Thung, Phang Nga, 27 June 1986 ; 3 WW, cl 7.0– 10.5 mm, 5 XX, cl 8.0– 9.5 mm (CU 1997.5), Kapong waterfall, Phang Nga, 21 June 1986 ; 1 W, cl 11.0 mm (CU 1997.6), Lumru waterfall, Kapong, Phang Nga, 12 July 1986 ; 37 specimens, cl 10.0–13.0 mm (CU 1997.21), Ton Sai waterfall, Thalang , Phuket, 8 April 1987 ; 2 WW, cl 9.0–12.0 mm, 2 ovigerous XX, cl 8.0–9.0 mm, 14 other specimens (CU 1997.23), Bag Pa waterfall, Thalang, Phuket, 14 October 1986 ; 10 WW, cl 8.0–13.0 mm, 2 ovigerous XX, cl 7.5–9.5 mm (CU 1997.25), Thap Put Tao Thong waterfall, Pang Nga, 27 March 1987 ; six specimens (CU 1997.68), no data; 1 W, cl 13.0 mm (CU 1997.127), Krabi, 28 October 1988 ; three specimens, Satun, coll. P. Naiyanetr, 22 March 1982 ; 2 WW, cl 10–105 mm (CU 1997.120), Nakhon Si Thammarat, coll. Pen Sak Tan, October 1976 ; 1 ovigerous X, cl 12.5 mm, 1 X, cl 18.5 mm (CU 1997.128), Nakhon Si Thammarat, 19 May 1976 ; one specimen, Nakhon Si Thammarat, 13 October 1988 ; four specimens (CU 1997.146), Chumphon, 23 July 1977 ; two specimens (CU 1997.148), Phatthalung, coll. P. Naiyanetr, 28 May 1976 ; four specimens (CU1997.149), Phuket, 18 May 1982 ; two specimens (CU 1997.150), Narathiwat, 28 May 1977 ; three specimens (CU 1997.151), Sawi , Chumphon, 12 December 1981 ; nine specimens (CU 1997.154), Surat Thani, coll. P. Naiyanetr, 27 March 1982 .

West Thailand. One W, cl 7.8 mm, 2 XX, cl 6.2–8.5 mm, 1 ovigerous X, cl 7.5 mm, eggs 1.0× 1.5 mm ( ZRC 2000.2682 ), Ratchaburi, Mae Nam Phachi at Ban Phachi, coll. M. Kottelat and K. Kubota, 2 April 1998 .

Thai specimens with no specific locality. One W, cl 7.5 mm, 1 X, cl 8.0 mm, 1 ovigerous X, cl 10.0 mm (CU 1997.53); 2 WW, cl 8.3–8.9 mm, 1 X, cl 11.5 mm, 1 ovigerous X, cl 7.0 mm, 2 WW, cl 13.4–15.0 mm (CU 1997.144).

Diagnosis

Rostrum short, straight or slightly convex, reaching to third segment of antennular peduncle or slightly beyond end of this segment; rostral formula 3–5+5–8/1–3, dorsal teeth more widely spaced posteriorly than anteriorly. Antennal spine sharp, hepatic spine small, situated below and behind antennal spine. Eyes well developed, large, about 0.25 times as long as carapace. Scaphocerite 2.7 times as long as broad, with straight outer margin. Epistome as in figure 19B. First to third abdominal sternites (figure 19C) with transverse ridge, with median tooth, that of first abdominal sternum largest, that of second small, that of third absent. First pereiopod with fingers slightly shorter than palm, chela 0.6 times as long as carpus. Male second pereiopods unequal in length; major male second pereiopod distinctively longer than body, covered with dense tufts of velvety pubescence on palm and fingers; fingers as long as or slightly longer than palm, with 7–10 large teeth on both cutting edges, not gaping when fingers closed; chela 4.8 times as long as carpus, carpus 1.4 times as long as wide. Third pereiopod reaching beyond scaphocerite by length of entire dactylus; propodus 2.6–3.0 times as long as dactylus. Uropodal diaeresis with a spine about half length of outer angle. Ovigerous females with eggs 1.0–1.1× 1.4–1.7 mm.

Remarks

With regards to its relatively larger eye, small egg size, and the fewer number of larger teeth and denticles on the cutting edges of the fingers, M. forcipatum can easily be separated from its closest congeners, M. hirsutimanus and M. eriocheirum (see Remarks on M. hirsutimanus and M. eriocheirum for details). Macrobrachium forcipatum can be distinguished from M. pilimanus by the form of rostrum, postorbital teeth occupying one-third the carapace length (versus 0.14–0.20 times), more widely spaced postorbital teeth (versus more closely spaced postorbital than anterior dorsal rostal teeth) and the fewer number of teeth on the cutting edges of the fingers of the male second pereiopod (7–10 versus 14–17). M. forcipatum is distributed in northern peninsular Malaysia and southern Thailand.