Macrobrachium

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 : 32-34

Macrobrachium sp.

( Fig. 19 )

Material examined. Vientiane Capital: Phatthana Village, 1 male (CL 11.0 mm), 22 Dec 2007, coll. school children & H. Ikenoue.

Diagnosis. Rostrum ( Fig. 19 a, tip broken) nearly straight, reaching anterior end of antennal scale, armed dorsally with 8 teeth, including 2 situated clearly posterior to orbital margin, ventral margin with 3 teeth; antennal spine arising just behind lateral margin, apex extending as far as end of antennal lobe; hepatic spine as large as antennal spine, placed posteriorly, just below level of antennal spine.

Sixth abdominal somite 1.54 times as long as fifth, pre-anal carina distinct, sub-triangular. Telson as long as sixth abdominal somite, posterior end triangular, with moderately large median projection, possessing 2 pairs of ordinary sub-terminal spines and 2 pairs of dorsolateral spines, anterior pair of latter ones situated just anterior to mid-length.

Antennal scale 0.8 times as long as carapace, 3.3 times as long as wide. Epistome without anteromedian lobe (bi-lobed).

First pereopod extending beyond antennal scale by length of chela. Second pereopods ( Fig. 19 a, b) sub-equal in length, shorter than entire body, extending beyond antennal scale by one-third of carpus and onwards; merus slightly longer than carpus, latter as long as palm; fingers 0.75 times as long as palm, without tubercles or teeth on cutting edges. Third pereopod ( Fig. 19 c, d) with propodus 2.8 times longer than dactylus.

Appendix masculina ( Fig. 19 e) with stiff setae on anterior margin and several setae aligned on mesial surface. Exopod of uropod ( Fig. 19 f) sub-equal in length to endopod, movable spine on diaeresis longer than lateral projection.

Remarks. This specimen was regarded as adult because its appendix masuculina ( Fig. 19 e) is well developed and superficially resembles M. tratense . However, it differs from the latter species in having a comparatively shorter rostrum, with fewer teeth on both the dorsal and ventral margins, and the second pereopod was proportionately shorter than that of the latter species (cf. Cai et al. 2004; Figs. 3–5 a). The present specimen also somewhat resembles the Chinese M. inflatum Liang & Yan, 1985 , in particular with regard to those reported from the Yunnan Province, south-eastern China (Cai & Dai 1999; Fig. 8 ). However, the palm of the second pereopod is distinctly longer than the fingers in the Laotian specimen while it is shorter or sub-equal length in M. inflatum . More materials are needed before its identity can be ascertained.

Figures

FIGURE 3. Macrobrachium dienbienphuense, male (CL 17.7 mm) collected from Luang Prabang Province, Laos, entire body. Scale bar = 10 mm.

FIGURE 4. Macrobrachium dienbienphuense, male (CL 12.5 mm) (a, g) and male (CL 14. 6 mm) (b – f) collected from Pakseng, Laos: a, entire body; b, epistome; c, fingers of second major pereopod, denuded, mesial view; d, propodus and dactylus of right third pereopod, lateral view; e, dactylus of same leg, lateral view; f, appendix masculina, mesial view; g, uropodal diaeresis, lateral view.

FIGURE 5. Genetic relationship of three species of the “ Macrobrachium dienbienphuense ” group inferred from the mitochondrial gene analysis (16 S rRNA).

FIGURE 8. Macrobracium mieni, male (CL 19.9 mm) from Kasi District, Vientiane Province (a, e), male (CL 20.0 mm) (c, d, f, g) collected from Kasi District, Vientiane Province, and male (CL 17.0 mm) (b) collected from Xuang River, Luang Prabang Province, Laos: a, entire body; b, epistome; c, left second pereopod, lateral view; d, basal part of chela of same leg, lateral view; e, propodus and dactylus of left third pereopod, lateral view; f, appendix masculina, mesial view; g, uropodal diaeresis, lateral view.

FIGURE 19. Macrobrachium sp., male (CL 11.0 mm) collected from Vientiane Capital, Laos: a, entire body; b, chela of left second pereopod, lateral view; c, propodus and dactylus of left third pereopod, lateral view; d, dactylus of same leg, lateral view; e, appendix masculina, mesial view; f, endopodal diaeresis, lateral view.