Macrobrachium sintangense ( De Man, 1898 )

Hanamura, Yukio, Imai, Hideyuki, Lasasimma, Oulaytham, Souliyamath, Pany & Ito, Sayaka, 2011, Freshwater prawns of the genus Macrobrachium Bate, 1868 (Crustacea, Decapoda, Palaemonidae) from Laos, Zootaxa 3025, pp. 1-37 : 20-23

Macrobrachium sintangense ( De Man, 1898)

( Figs. 11 , 12 )

Palaemon (Eupalaemon) sintangensis De Man, 1898: 138 , pl. 6.

Macrobrachium sintangense: Holthuis 1950: 151 ; Ng 1994: 77, fig. 6; Cai et al. 2004: 592, fig. 2; Nguyen 2006: 235 –253, figs. 2c, d, 3k, l.

Material examined. Luang Prabang Province: Mekong River, Pakxeng Village, 1 male (CL 17.5 mm) 2 females (CL 13.0 mm, 13.3 mm), March 2001, coll. O. Lasasimma (LARReC C012, as Macrobrachium sp. 3). Champasak Province: Det Island, 3 males (CL 7.1–8.7 mm), 1 female (CL 9.8 mm), 11 July, 2009, set net, coll. S. Ito & Y. Niimura; Khone Island, 1 male (CL 10.4 mm), 10 July 2009, set net, coll. S. Ito & Y. Niimura; Det Island, 6 males (CL 9.1–18.0 mm), 14 females (CL 13.5–16.2 mm), 5 ovig. females (CL 12.5–16.5 mm), set net, 21 July 2009, coll. Y. Niimura; Det Island, 1 male (CL 8.0 mm), 2 females (CL 8.2 mm, 8.4 mm), 1 ovig. female (CL 12.0 mm), set net, 23 July 2009, coll. Y. Niimura.

Diagnosis. Rostrum ( Figs. 11 a, b, 12a, b) fully reaching or extending well beyond anterior end of antennal scale, dorsal margin weakly or distinctly curving dorsad, armed dorsally with 10–12 teeth including 2 or 3 placed posterior to orbital margin, ventrally with 4 or 5 teeth; antennal spine placed just behind lateral margin, apex extending beyond end of antennal lobe; hepatic spine as large as antennal spine, placed posteriorly, just below level of antennal spine.

Sixth abdominal somite 1.25–1.45 times as long as fifth one; pre-anal carina poorly developed but traceable as obtuse swelling. Telson 1.65–1.85 times as long as sixth abdominal somite, ending in moderately sharp median projection, with 2 pairs of ordinary sub-terminal spines and 2 pairs of dorsolateral spines, anterior pair of latter ones situated at mid-length or just beneath it.

Antennal scale 0.7–0.75 times as long as carapace, about 3 times as long as wide.

Second male pereopods sub-equal in length, slender and slightly longer than total body length, with mero-carpal articulation barely reaching anterior end of antennal scale, with minute spinules on almost its entire length; merus shorter than carpus; carpus slightly longer than palm; fingers ( Figs.11 c, 12c) about two-thirds length of palm, its basal half covered with short velvety setae, no grooves present; cutting edge of movable finger with 2 teeth and that of fixed finger with single tooth near basal part. Third pereopod ( Figs. 11 d, e, 12d) with propodus about 3.0–3.9 times as long as dactylus.

Appendix masculina ( Figs. 11 f, 12f) slightly less than twice length of appendix interna, with moderately long setae on anterolateral margin and several stiff setae scattered on mesial surface. Exopod of uropod ( Figs. 11 g, 12g) slightly longer than endopod, movable spine on diaeresis as long as or slightly longer than lateral projection.

Egg. Eyed-eggs about 1.0–1.1 x 1.5–1.8 mm

Remarks. In our specimens, males larger than 16 mm in carapace length had velvety setae on the fingers of the second pereopods, although the second legs showed some variations in their morphological structure depending on specimens. Females of comparable body size had proportionately shorter second pereopods than males and did not bear velvety setae except for one female of 14.5 mm in carapace length with scattered fine setae. Moreover, the second pereopods of young males and females were variable in ornamentation, from nearly smooth to spinous. Thus, the ornamentation (velvety setae and teeth/protuberances) of the second pereopod seemed to develop only in late stages of life. Hence, sub-adult specimens (cf. Fig. 12 ) showed a closer resemblance to M. tratense established by Cai et al. (2004) from Thailand.

Ng (1994) recorded this species from the Sabah, eastern Malaysia, which was followed by Cai et al. (2004). The rostrum of Ng’s (1994) specimens had more widely set teeth on the ventral margin, and this may suggest that they are not con-specific. Cai et al. (2004) noted that the taxonomy of M. sintangense (type locality central Borneo) may not be so straightforward as a synonym, Palaemon elegans De Man, 1892 (type locality Java), is probably a valid species.

Macrobrachium sintangense resembles M. saigonensis Nguyen, 2006 recorded from southern Vietnam. According to Nguyen (2006), M. saigonensis has much larger body size and second pereopod than others in this species and bears smaller eggs ( Nguyen, 2006). Furthermore, M. sintangense occurs entirely in fresh waters, while M. saigonensis inhabits slightly haline waters (0–12 in salinity).

Distribution. Known with reasonable certainty from Borneo, Peninsular Malaysia, and Thailand, through Yunnan, and now in Laos ( Liu et al. 1990; Cai & Dai 1999; Cai et al. 2004; present study). Macrobrachium sintangense is exploited for human consumption in southern Laos.

Figures

FIGURE 11. Macrobrachium sintangense, male (CL 17.5 mm) collected from Pakxeng, Luang Prabang Province, Laos: a, entire body; b, anterior part of carapace and cephalic appendages, lateral, view; c, fingers of left second pereopod, lateral view; d, propodus and dactylus of left third pereopod, lateral view; e, dactylus of same leg, lateral view; f, appendix masculina, mesial view; g, uropodal diaeresis, lateral view.

FIGURE 12. Macrobrachium sintangense, male (CL 10.4 mm) collected from Khone Island, Champasak Province, Laos: a, entire body; b, epistome; c, chela of left second pereopod, lateral view; d, propodus and dactylus of right third pereopod, lateral view; e, appendix masculina, mesial view; f, uropodal diaeresis, lateral view.