(figure 2)

Palaemon (Eupalaemon) sintangensis De Man, 1898: 138, pl. 6 [type locality: Sintang, Kapuas river, Borneo].

Palaemon nipponensis: Lanchester, 1902: 566 (not P. nipponensis De Haan, 1849).

Palaemon elegans: Kemp, 1918a: 264 (not P. elegans De Man, 1892).

Macrobrachium elegans: Suvatti, 1937: 49; 1967: 139.

Macrobrachium sintangense: Holthuis, 1950: 151; 1980: 105; Johnson, 1968: 236; Lumubol, 1980: 502, figure; Naiyanetr, 1980: 17; 1992: 18, 1998: 33. Chace and Bruce, 1993: 38; Ng, 1995: 189; figure 6; not Macrobrachium sintangense: Kamita, 1974: 7.

Material examined

Central Thailand. Forty-nine WW, cl 11.0– 16.5 mm, 1 X, cl 10.5 mm, 6 ovigerous XX, cl 10.0–12.0, eggs 1.3× 0.9 mm (ZRC 2000.2635), Lop Buri Province, Chai Badan, coll. Y. Cai, 20 June 1998; 115 specimens, cl 5.0– 15.3 mm (CU 1997.222), Phetchabun, 22 May 1982; 5 WW, cl 14.4–19.9 mm, Saraburi, no date; 1 W, cl 15.8 mm, 1 X, cl 14.0 mm (CU 1997.887), Saraburi, 18 Jun 1980; 2 WW, cl 12.4–15.0 mm, 3 XX, cl 11.2–12.7 mm (CU 1997.228), Suphan Buri, 30 June 1980; 15 specimens (ZRC 2000.2651), Khoksamrong Market, 54 km from Chai Badan, coll. Y. Cai and Y. Y. Goh, 20 June 1998.

West Thailand. Three WW, cl 11.8–13.8 mm, 30 small specimens (ZRC 2000.2650), Thailand, Prachuap Khiri Khan Province, Kui Buri District, stream near Ban Yang Chum, 12°3∞18.7◊N, 99°37∞44.2◊E, coll. D. Yeo et al., July 1997.

North-east Thailand. One W, cl 19.6 mm (ZRC 2000.2636), Mekong river at Udon Thani, 17°47∞57.2◊N, 102°28∞59.5◊E, coll. Y. Cai, 19 June 1998; 5 WW, cl 10.5–12.2 mm, 6 XX (3 ovigerous X, egg diameter: 1.2× 0.9 mm) (CU 1997.169), Rayong, 6 December 1981, coll. S. Panha; 1 W, cl 9.6 mm (broken rostrum), 1 X, cl 9.0 mm (CU 1997.7), Yasothon, 12 March 1994; 30 specimens (ZRC 2000.2677), Warin Chamrap Market, coll. Y. Cai, 17 June 1998; 10 specimens (ZRC 2000.2637), Phibun Mangsahan Market, 46 km east to Ubon Rachathani, coll. Y. Cai, 16 June 1998; 10 specimens (ZRC 2000.2639), Ban Nan Khaisat, artificial lake for rice field, 50 km to Bung Kan, coll. Y. Cai and Y. Y. Goh, 18 June 1998; 10 specimens (ZRC 2000.2680), Khoksamrong Market, 54 km from Chai Badan, coll. Y. Cai and Y. Y. Goh, 20 June 1998.

East Thailand. Fifty-eight specimens (CU 1997.115), Chanthaburi, 9 February 1990; 21 specimens, Rayong, coll. S. Panha, 6 December 1981; 1 W, cl 17 mm (ZRC 2000.2712), Trat Province, stream at Ban Kraduk Chang road 3157 from Trat to Bora, 1–2 km after junction with road 3271, coll. M. Kottelat et al., 12 March 1993.

South Thailand. Three WW, cl 5.6–10.0 mm (ZRC 2000.2629), 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., 1998; 6 WW, cl 6.0–12.0 mm, 1 X, cl 10.5 mm, 2 ovigerous XX, cl 11.0 mm, egg size 1.2×1.0 mm (ZRC 2000.2632), Satun Province, stream in Ban Kong Kruat, pH 6.0, coll. M. Kottelat, 4 November 1995; 2 ovigerous XX, egg size 0.8× 0.6 mm (ZRC 2000.2630), 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; 3 WW, cl 9.5–13.2 mm, 2 XX, cl 6.5–7.5 mm, 6 ovigerous XX, cl 9.5–10.5 mm, eggs with eye spot, eggs 0.9× 0.6 mm (ZRC 2000.2642), Narathiwat Province, Nam Tok Sipo, downstream area, 6°16.06∞N, 101°38.65∞E, coll. H. H. Tan et al., 24 October 1998; 4 WW, cl 9.0– 14.8 mm, 4 XX, 8.0– 10.5 mm, 10 ovigerous XX, cl 11.5–12.5 mm, eggs with eyes, 1.5×1.0 mm (ZRC 2000.2641), 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, pH 6.8, coll. M. Kottelat, 2 November 1995; 5 WW, cl 10.3–16.0 mm, 1 ovigerous X, cl 9.3 mm (ZRC 2000.2640), Satun Province, stream in Ban Kong Kruat, pH 6.0, coll. M. Kottelat, 4 November 1995; 1 W, cl 13.0 mm (CU 1997.11), Thai Muaug, Phang Nga, 28 August 1986; 1 X, cl 15.0 mm, 50 WW, cl 17.0– 19.5 mm (CU), Phatthalung, 27 October 1982; 4 WW, 2 XX (CU 1997.104), Songkhla, coll. P. Naiyanetr, 11 April 1983; 3 WW (CU 1997.105), Trang, 29 October 1988; 6 WW, cl 10.3–11.0 mm, 2 ovigerous XX, cl 9.6–9.7 mm, Ubon Rathathani, 1 April 1980; 76 specimens, cl 10.1–21.0 mm (CU 1997.229), Songkhla, 7 November 1982; 2 WW, cl 7–14 mm (CU), Krabi, coll. P. Naiyanetr, 9 December 1986.

Thai specimens with no specific locality. Nine XX, cl 10.5–14.6 mm (all ovigerous) (CU 1997.223); 1 W, cl 16.0 mm, 1 X, cl 15.5 mm, (CU 1997.97); 1 X, cl 13.0 mm (CU 1997.107); 2 XX, 8 ovigerous XX, cl 6.2–9.7 mm (CU 1997.188); 2 WW, CU 1997.105, Trang, 29 October 1988; 1 W, cl 13.0 mm (CU 1997.90); 2 WW, cl 11.2–12.5 mm (CU 1997.8).

Diagnosis

Rostrum varying from convex to straight or slightly upturned anteriorly, reaching to or slightly beyond end of scaphocerite, rostral formula: 2–3+6–10(7–8)/2–5(2–3), dorsal teeth unevenly spaced; first pereiopods with carpus twice as long as chela; second pereiopods subequal in length, similar in form, carpus longer than merus, shorter than chela; fingers equal to or slightly longer than palm in young, shorter than palm in adults; two small teeth present on proximal third or fourth of cutting edge of fingers; adult males with distinct pubescence on proximal half to two-thirds of fingers; a row of tubercles on each side of cutting edge of dactylus; small spinules present on all joints of adult chelipeds.

Remarks

Macrobrachium sintangense is characterized by the fingers of the second pereiopod, with the proximal half densely covered with short setae in adult. The present Thai specimens agree well with De Man’s original description with the exception of the rostral form. The rostrum of the type specimens (fide De Man, 1898) is straight, while those of the Thai specimens are only straight along the posterior part, with the anterior fifth distinctively upcurved. Macrobrachium sintangense has been reported from Thailand by Kemp (1918a), Suvatti (1937), Holthuis (1950), Lumubol (1980) and Naiyanetr (1980). Lanchester (1902) reported Palaemon nipponensis De Haan, 1849, from southern Thailand, but Holthuis (1950) pointed out that Lanchester’s specimens are actually M. sintangense instead. Johnson (1963) stated that M. sintangensis inhabits slow-flowing rivers, canals and streams, being more common in open and disturbed sites than forest areas. Johnson (1966) also added that this species requires moderately hard water and cannot be found in waters with very low oxygen content.

Johnson (1968: 236) remarked that in Malaysia this species ‘appears to have potential economic value’. In Thailand, it is a common species and is sold in the markets along the Mekong.

Kamita (1974) reported M. sintangense from Nepal, but according to his description and illustration, the rostral form, slightly compressed palm, the fingers having grooves, and being pubescent at the proximal half of cutting edges, his specimens should be referred to M. dayanum instead.

Macrobrachium sintangense is known with certainty from Borneo, peninsular Malaysia and Thailand. With the shorter convex rostrum, which does not reach beyond the end of antennular peduncle and the more prominent pubescence on the fingers of second pereiopods, P. elegans De Man, 1892, which has long been synonymized with M. sintangense, should be regarded as a distinct species (D. Wowor, personal communication).