Macrobrachium eriocheirum Dai, 1984

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 : 10-11

Macrobrachium eriocheirum Dai, 1984

( Fig. 6 )

Macrobrachium eriocheirum Dai, 1984: 247 , fig. 13; Cai & Dai 1999: 230, fig. 13; Cai et al. 2004: 628, fig. 18a–d. Macrobrachium dienbienphuense: Li et al. 2007: 84 (part).

Material examined. Luang Praban Province: Ou River, Ngoi District, 7 males (CL 9.8–13.3 mm), 2 females (CL 9.8 mm, 10.1 mm), Sept 2000, coll. O. Lasasimma (ex LARReC C 0002); Ou River, Ngoi District, 2 males (CL 12.0 mm, 15.0 mm), Feb 2001, coll. O. Lasasimma (ex LARReC C 0004); Ou River, Ngoi District, 3 males (CL 12.5–13.8 mm), Feb 2001, coll. O. Lasasimma (ex LARReC C 0006); Ou River, Ngoi District, 3 males (CL 13.5– 15.8 mm), 5 ovig. females (CL 10.5–13.0 mm), Feb 2001, coll. O. Lasasimma (LARReC C 0007); Ou River, Ngoi District, 1 male (CL 13.5 mm), 1 female (CL 11.4 mm), 4 ovig. females (CL 9.8–12.2 mm), Feb 2001, coll. O. Lasasimma (LARReC C 0009); Xuang River, Na Pho Village, St. 2, 10 males (CL 6.2–15.2 mm), 28 females (CL 5.8–11.1 mm), 28 Jan 2008, hand net, coll. S. Ito et al.; Xuang River, Na Pho Village, St. 1, 1 males (CL 11.0 mm), 27 Mar 2008, hand net, coll. S. Ito et al.; Xuang River, Na Pho Village, St. 3, 2 males (CL 13.0 mm, 14.0 mm), 27 Mar 2008, hand net, coll. S. Ito et al.; Xuang River, Na Pho Village, St. 2, 2 males (CL 12.7 mm, 15.2 mm), 1 ovig. female (CL 10.3 mm), 27 Apr 2008, hand net, coll. S. Ito et al. Savannakhet Province: Sampling details unknown, 8 males (CL 10.5–12.1 mm), 1 female (CL 10.2 mm), 5 females (CL 7.8–11.2 mm), 2002; Kae Stream, 6 males (CL 11.5–15.7 mm), other details unknown. Champasak Province: Khone Island, 1 male (CL 12.7 mm), 11 July 2009, set net, coll. S. Ito & Y. Niimura.

Diagnosis. Rostrum ( Fig. 6 a) reaching or slightly overreaching end of antennal scale, 0.4–0.6 times as long as carapace, dorsal margin weakly convex, directed slightly ventrad, armed dorsally with 11–14 teeth including 4–6 placed posterior to orbital margin, ventral margin with 2 or 3 teeth; antennal lobe moderately produced, antennal spine slightly extending beyond antennal lobe; hepatic spine as large as or slightly smaller than antennal spine, situated posteriorly, distinctly below level of antennal tooth.

Abdomen ( Fig. 6 a) with sixth somite 1.2–1.5 times as long as fifth; pre-anal carina well developed; fourth pleuron rounded posteroventrally, that of fifth angulated. Telson 1.38 times as long as sixth somite, with sub-triangular posterior end, with pairs of ordinal small and long sub-distal spines and 2 pairs of dorsolateral spines, anterior pair of latter spines placed at or just posterior to mid-length.

Antennal scale 0.5–0.6 times as long as carapace, slightly more than 2.5 times longer than wide. Epistome usually with marked anteromedian projection (tri-lobed in form) but rarely indistinct. Third maxilliped falling well short of anterior end of antennular peduncle, distal segment slightly shorter than penultimate.

First pereopod extending beyond antennal scale by distal 0.3–0.5 length of carpus and onwards, fingers as long as or slightly shorter than palm. Second pereopods ( Fig. 6 a–c) distinctly unequal in length, covered with long, dense velvety setae normally on palm and fingers: major leg longer than total body length, extending beyond antennal scale by carpus and onwards; merus as long as palm, 2.9–3.9 times as long as high, with microscopically small spinules particularly on dorsal and lateral surfaces; carpus somewhat cup-shaped, normally less than 2.0 times as long as high, with minute spinules particularly on lateral and dorsal surfaces; palm as long as or slightly shorter than fingers, 2.2–2.8 times as long as wide; fingers with narrow gape when crossed, with 11–17 teeth on cutting edges; minor leg extending beyond antennal scale by chela, palm slightly more than 1.5 times as long as fingers and again slightly more than 2 times as long as wide. Third pereopod with propodus ( Fig. 6 d) 2.3–2.9 times as long as dactylus, with 5 or 6 sparsely placed spines on posterior margin.

Appendix masculina ( Fig. 6 e) about twice length of appendix interna, with numerous stiff setae on mesial surface as well as anterolateral margin. Uropodal exopod ( Fig. 6 f) sub-equal in length to endopod, movable spine on diaeresis shorter than lateral projection.

Egg. Eggs fewer in number but large in size, non-eyed eggs measuring 1.0–1.25 x 1.4–1.7 mm.

Remarks. As has been mentioned above, the exact identification of species of the “ M. dienbienphuense ” group has often been difficult using just morphology, especially in immature and female specimens due to intra-specific variations and ontogenetic morphological changes, the measurements and comparison data in fully grown specimens assigned to M. eriocheirum , M. amplimanus , and M. dienbienphuense were summarised in Table 2 , and they suggest all three are distinct. Furthermore, M. eriocheirum appeared to bear proportionately larger eggs than those of the two congeners. The morphological data were supported by the mitochondrial gene (16S rRNA) analysis, as it yielded three clearly different clades that could be regarded as the three distinct species ( Fig. 5 ), although the M. eriocheirum clade has genetically high intra-specific divergences.

In our personal examination, 42% of Laotian specimens (N=78) were right-handed, with the right second pereopod being larger than the left one (Hanamura et al. unpubl. data).

Distribution. Yunnan Province, south-western China, Thailand, and Laos ( Dai 1984; Cai & Dai 1999, Cai et al. 2004; present study). Macrobrachium eriocheirum appeared to be one of the most abundant species along the Mekong River system in Laos.

Figures

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

FIGURE 6. Macrobrachium eriocheirum, male (CL 15.2 mm) (a, b, d – f) and male (CL 15.8 mm) (c) collected from Xuang River, Luang Prabang Province, Laos: a, entire body; b, carpus to dactylus of left major second pereopod, mesial view; c, fingers of right major second pereopod, denuded, mesial view; d, right third pereopod, lateral view; e, appendix masculina, mesial view; f, uropodal diaeresis, lateral view.