Macrobrachium thai Cai, Naiyanetr & Ng, 2004

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 : 27-28

Macrobrachium thai Cai, Naiyanetr & Ng, 2004

( Fig. 15 )

Macrobrachium thai Cai, Naiyanetr & Ng, 2004: 605 , figs. 8, 9.

Material examined. Khammouane Province: Theun River, 6 males (CL 4.2–9.4 mm), 7 females (CL 4.0– 12.2 mm), 2 juvs. (CL 3.5 mm, 3.8 mm), 13 July 2009, hand net, coll. S. Ito & Y. Niimura. Savannakhet Province: Sampling details unknown, 2 ovig. females (CL 8.7 mm, 9.2 mm), 2002. Champasak Province: Det Island, 1 male (CL 7.4 mm), 2 females (CL 6.5 mm, 7.2 mm), 10 July 2009, hand net, coll. S. Ito & Y. Niimura.

Diagnosis. Rostrum ( Fig. 15 a) barely reaching anterior end of antennal scale, dorsal margin nearly straight, with 8–11 teeth including 2 or 3 placed posterior to orbital margin, ventral margin with 2 or 3 teeth; antennal spine sub-marginal, apex slightly extending beyond antennal lobe, carina supporting antennal spine moderately long; hepatic spine smaller than antennal spine, placed just below level of antennal spine.

Sixth abdominal somite 1.4–1.55 times as long as fifth somite, fourth pleuron rounded posteroventrally, that of fifth sub-rectangular; pre-anal carina well marked, sub-triangular in shape. Telson 1.35–1.55 times as long as sixth abdominal somite, ending in short but sharp process, with 2 pairs of ordinary sub-terminal spines and 2 pairs of dorsolateral spines, anterior pair of latter ones situated at mid-length.

Antennal scale 0.7–0.75 times as long as carapace, 2.9–3.1 times as long as wide. Epistome ( Fig. 15 b) bilobed.

First pereopod extending beyond antennal scale by fingers, latter as long as palm. Second pereopods ( Fig. 15 a, c) rather slender, sub-equal in length, shorter than total body length, extending beyond antennal scale by distal half of carpus and onwards; merus as long as or slightly longer than carpus, latter as long as or slightly shorter than palm; fingers 0.75–0.9 times as long as palm, cutting edges with about 6 obtuse teeth on proximal part. Third pereopod with propodus ( Fig. 15 d) 2.5–3.1 times as long as dactylus, possessing 6–8 spines on posterior margin.

Appendix masculina about twice length of appendix interna, with numerous stiff setae on anterolateral margin and mesial surface. Uropod with exopod sub-equal in length or slightly longer than endopod, movable spine on diaeresis ( Fig. 15 e) slightly longer than lateral projection.

Egg. Eggs oblong, non-eyed eggs measuring 1.1–1.2 x 1.7–1.8 mm.

Remarks. Our specimens agreed with the original description of this species, although the Laotian specimens had a comparatively shorter dactylus of the third pereopod. The material examined also resembled M. niphanae , but a proportionately slender and short second pereopods with a naked, smooth carpus distinguishes it from the latter species. Macrobrachium thai also resembles M. tratense , but the rostrum of this species was consistently shorter than that of the latter species, not extending beyond the antennal scale.

Distribution. Macrobrachium thai has been recorded from north-eastern and eastern Thailand (Cai et al. 2004) and also in southern Laos (present study).

Figures

FIGURE 15. Macrobrachium thai, male (CL 9.4 mm) collected from Thyun River, Khammouane 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.