Macrobrachium thai, Cai & Naiyanetr & Ng, 2004

Cai, Y., Naiyanetr, P. & Ng, P. K. L., 2004, The freshwater prawns of the genus Macrobrachium Bate, 1868, of Thailand (Crustacea: Decapoda: Palaemonidae), Journal of Natural History 38 (5), pp. 581-649 : 605-609

Macrobrachium thai sp. nov.

(figures 8, 9)

Material examined

H: W, cl 14.0 mm, Nong Khai, north-east Thailand, 14 December 1990 ( ZRC 2000.2648 ) .

P: 6 WW, cl 10.5–14.0 mm, 8 XX, cl 10.0–13.0 mm (CU 1997.99), same data as holotype.

Other specimens. Central Thailand. Nine specimens (CU 1997.173), Kaeng Khoi, Saraburi, no date.

East Thailand. Two WW, cl 10.5–11.0 mm (CU 1997-106), Prachinburi, coll. P. Naiyanetr, 28 October 1980 .

North-east Thailand. Eight WW, cl 10.2–14.3 mm, 1 ovigerous X, cl 8.8 mm ( ZRC 2000.2713 ), Yasothon, 12 March 1994 ; 6 WW, cl 8.8–10.3 mm, 4 ovigerous, XX, cl 5.7–5.8 mm, 21 specimens, cl 7.5–9.5 mm ( ZRC 2000.2721 ), Phibun Mangsahan Market, 46 km east to Ubon Rachathani , coll. Y. Cai, 16 June 1998 ; 64 WW, cl 6.8–8.8 mm, 26 ovigerous XX, cl 6.5–7.5 mm, eggs 1.7× 0.9 mm ( ZRC 2000.2679 ), Khan Tit, 800 m turn off from Wiang Bun, 90 km to Chiang Khan , small stream 0.1–0.5 m in depth, 1–3 m in width, near a bamboo forest and rice field, 18°7∞49.8◊N, 102°11∞0.5◊E, coll. Y. Cai et al., 19 June 1998 ; 14 WW, cl 6.5–9.8 mm, 5 XX, cl 8.5–13.6, 5 ovigerous XX, cl 10.6–12.0 mm, eggs with eyes, 1.4× 0.95 mm ( ZRC 2000.2724 ), Warin Chamrap Market , coll. Y. Cai, 17 June 1998 ; 12 WW, cl 6.5–9.0 mm, 4 XX, cl 9.0– 13.5 mm, 5 ovigerous XX, cl 10.5–12 mm ( ZRC 2000.2714 ), Phulangka waterfall (Nam Tok) National Park , downstream grass and hard mud bank, flooded-covering 1 m aside ground grass, cool water, 17°57∞18.9◊N, 104°09∞35.8◊E, coll. Y. Cai and Y. Y. Goh, 18 June 1998 ; 9 WW, cl 7–11 mm, 6 XX, cl 7–10 mm, 14 ovigerous XX, cl 7.5–11.5 mm, 37 juveniles ( ZRC 2000.2725 ), lake 20 km south from Nakhon Phanom, pH 6.6, coll. Y. Cai and Y. Y. Goh, 17 June 1998 .

Description

Rostrum (figures 8A, 9A, B) straight, reaching to distal end of scaphocerite, tip slightly upturned; rostral formula: 2–3 (mode 2)+5–8 (mode 6–7)/2–3 (mode 3). Teeth placed more widely posteriorly than anteriorly. Antennal spine below inferior orbital angle, hepatic spine small, located just behind antennal spine, nearly at same level. Antennular peduncle about 0.6 times as long as carapace. Antennal spine sharp, situated below lower orbital angle. Carapace smooth.

Fourth thoracic sternite without median process. Abdomen (figure 8A) smooth, glabrous, first to third pleurites broadly rounded, fourth and fifth feebly produced posteriorly, fourth subtriangular, fifth subrectangular; sixth abdominal somite 1.3 times as long as fifth one, with posteroventral angle feebly produced, subacute. Telson (figure 9E) 1.2 times as long as sixth abdominal segment, with two pairs of dorsal spines, ending in a small acute median point, latter spines small, smaller than dorsal spines, intermediate spines well developed, with about six pairs of long plumose setae. First to third abdominal sternites (figure 9D) with transverse ridge and a median tooth, that of second abdominal sternite most prominent, that of first abdominal sternite less prominent, that of third one smaller than previous two. Preanal region with small ridge, smooth.

Eyes (figure 9A, B) well developed, cornea longer, broader than stalk. Basal segment of antennular peduncle broad. Stylocerite distinctly pointed, reaching middle of basal segment. Antenna (figure 9F) with stout basicerite, with strong distoventral tooth, carpocerite reaching to about 0.4 times of scaphocerite length. Scaphocerite slender, about four times as long as wide, with straight outer margin.

Epistome as in figure 9C, bilobed by a shallow depression. Mouthparts typical of genus (figure 8B–H).

First pereiopod (figure 9G) reaching beyond distal end of scaphocerite by entire chela, propodus 2.6 times as long as chela, chela with fingers as long as palm. Second pereiopods (figures 9H, I) of male unequal in length, similar in form. Major second pereiopod distinctively longer than body length, reaching with one-sixth length of carpus beyond distal end of scaphocerite, carpus slightly shorter than, or as long as merus, distinctively shorter than palm; fingers short, about 0.3–0.4 times length of palm, cutting edge with a row of 10–20 small teeth at proximal two-thirds or along entire cutting margin. Minor second pereiopod about same length as body. Third pereiopod (figure 9J, K) reaching end of scaphocerite, propodus nine times as long as broad, 4.2 times as long as dactylus; dactylus 3.5 times as long as wide, terminating in small claw.

Uropodal diaeresis with a spine (figure 9L) longer than outer angle. Ovigerous female with egg 1.55× 1.10 mm in diameter.

Etymology

Macrobrachium thai is named after the type locality. The name is used as a noun in apposition.

Habitat

The present new species was found from mountain streams and small rivers in central and north-eastern Thailand.

Remarks

With respect to the form of the rostrum and second pereiopod, Macrobrachium thai sp. nov. is most similar to M. vietnamense Dang, 1975, described from northern Vietnam. Macrobrachium thai can, however, easily be distinguished from M. vietnamense by the rostrum, which has fewer postorbital teeth (two to three, mode two versus four); the smaller egg size (1.55× 1.1 mm versus 1.9–2.0× 1.3–1.45 mm) and the teeth along the cutting edges of the fingers of the second pereiopod possessing a row of 10–13 small teeth (versus with only two large teeth) (cf. Dang, 1975). Macrobrachium thai is also similar to M. mieni Dang, 1975 , from Vietnam, central and north-east Thailand in the form of rostrum and the second pereiopods, but can be differentiated by the fingers of the second pereiopod having more teeth on the cutting edge (10–20 versus 8–10); the propodus of the third pereiopod is 4.2 times as long as the dactylus (versus 3.4 times), and the movable spine on the uropodal diaeresis is longer than outer angle (versus shorter).