Macrobrachium tratense, 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 : 595-598

Macrobrachium tratense sp. nov.

(figures 3, 4, 5A)

Material examined

H: W, cl 16.4 mm ( ZRC 1997.129 ), Khlong Fuai, road 3271, 12°23∞44.8◊N, 102°39∞34.5◊E, Trat Province, coll. H. H. Tan et al., 15 January 1997 .

P: 5 WW, cl 12.5–16.8 mm; 5 XX, cl 8.0– 11.2 mm (ZRC 2000.2734), eggs 1.1–1.15× 0.8–0.9 mm, same data as holotype.

Others. Three WW, cl 13–16 mm, 2 XX, cl 11–12 mm ( ZRC 1997.123 ), Klong Pheet (stream), ca 35 km from Trat, Chantaburi Province, 12°28∞04.5◊N, 102°37∞07.1◊E, coll. H. H. Tan et al., 14 January 1997 ; 4 XX, cl 9.5–12.5 mm ( ZRC 2000.2704 ), Trat Province, Khlong Huai Raeng, km 18 on road 3271 from Trat to Bo Rai , coll. M. Kottelat et al., 3 December 1993 ; 2 WW, cl 13.5–14.0 mm, 2 XX, cl 12–17 mm ( ZRC 2000.2688 ), Trat Province, Khlong Huai Raeng, km 18 on road 3271 from Trat to Bo Rai , coll. M. Kottelat et al., 3 December 1993 .

Description

Rostrum (figure 4A) straight at base, upcurved along anterior one-quarter of its length, reaching beyond end of scaphocerite, as long as carapace length, dorsal margin of rostrum with 9–12 teeth (mode 11), ventral with five to six (mode 5), two to three (mode two) dorsal teeth behind postorbital margin, occupying about one-third to one-quarter length of carapace, postorbital teeth more widely spaced than others. Antennal spine sharp, situated below inferior orbital angle. Hepatic spine smaller than antennal spine, lying behind and slightly below latter. Carapace smooth.

Third thoracic sternite with indistinct transverse ridge, fourth thoracic sternite with median process (figure 4D). Abdomen (figure 3A) smooth, glabrous, first to third pleurites broadly rounded, fourth and fifth feebly posteriorly produced, fourth subtriangular, fifth subrectangular, sixth abdominal somite 1.6 times as long as fifth, posterolateral angle strongly produced, acute, posteroventral angle feebly produced, subacute. Telson (figure 4F) 1.4 times length of sixth abdominal segment, with two pairs of small dorsal spines, ending in a small acute median point, lateral spines small, smaller than dorsal spines, intermediate spines well developed, with several pairs of long plumose setae. First to third abdominal sternites with transverse ridge, with median tooth in first two (figure 4E), that of second abdominal sternite larger, pointed, that of third sternite less prominent, fourth and fifth sternite with indistinct bluntly triangular ridges. Preanal region unarmed.

Eyes well developed, cornea longer, broader than stalk. Basal segment of antennular peduncle broad. Stylocerite distinctly pointed, reaching middle of basal segment. Anterolateral tooth reaching about middle of second segment. Second segment as long as third segment. Scaphocerite (figure 4B) 3.3 times as long as broad, with straight outer margin.

Epistome as in figure 4C, bilobed by a shallow depression.

Mouth parts as in figure 3. Mandibular palp slender, three-segmented; incisor process robust; metastoma with paragnathus (figure 3B) proximally fused forming a broad corpus with well-developed anterior median depression, paragnaths distally bilobed, upper lobe large, elliptical. Maxillular (figure 3D) palp bilobed, upper lobe slender, lower lobe stout; maxilla (figure 3E) with simple palp, basal endite deeply bilobed, scaphognathite normal; first maxilliped (figure 3F) with setose palp, basal and coxal endites distinct, flagellum of exopod with numerous plumose setae distally, epipod deeply bilobed; second maxilliped (figure 3G) with normal endopod, flagellum with numerous plumose setae distally, epipod simple, with well-developed podobranch; third maxilliped (figure 3H) with robust endopod, exopod with numerous plumose setae distally, reaching to distal margin of ischiomerus.

First pereiopod (figure 4G) very slender, reaching beyond scaphocerite by entire chela, equal in length, similar in form. Palm as long as fingers, carpus 2.4 times as long as chela, merus slightly shorter than carpus, twice as long as ischium. Male second pereiopods (figures 4H, I) equal in length, similar in form. Second pereiopod reaching beyond scaphocerite by carpus, slightly shorter or as long as total body length. Fingers of chela straight, with curved pointed tips, not gaping when closed, cutting edges with sharp ridges except one or two indistinctive denticles proximally at base; slightly shorter than palm. Palm cylindrical, 5.3 times as long as broad. Carpus longer than palm, conical. Merus slightly shorter than palm. Last three pereiopods slender, similar in form. Third pereiopod (figure 4J, K) reaching beyond scaphocerite by one-third of carpus. Dactylus relatively short but slender, 5.7 times as long as broad. Propodus 3.3 times as long as dactylus, with about 10 spinules on posterior margin. Fifth pereiopod more slender than third one, reaching end of antennular peduncle.

Endopod of male first pleopod with inner margin concave, outer margin convex. Appendix masculina of male second pleopod longer, stouter than appendix interna, with numerous stiff spines.

Uropodal diaeresis with inner movable spine, longer than outer angle. Egg size 0.8–0.9× 1.1–1.2 mm in diameter.

Etymology The species is named after the type locality, Trat Province, East Thailand.

Habitat

Macrobrachium tratense was collected from mountain streams from and near Trat, East Thailand.

Remarks

Macrobrachium tratense sp. nov. morphologically resembles M. inflatum Liang and Yan, 1985 , which was originally described from Kunshan, Jiangsu Province, in eastern China and recently recorded from Xishuangbanna of Yunnan Province (Cai and Dai, 1999). However, it differs from M. inflatum (figure 5B–F, M, cl 15.5 mm, paratype, SFU 57-48-04, Kunshan County, Jiangsu Province, eastern China, coll. Liang and Yan, April 1957) by the rostral formula, which has more ventral teeth (five to six versus two to four in M. inflatum ); the shorter dactylus on third pereiopod (propodus 3.3 times as long as dactylus versus 2.5 times in M. inflatum ); and the longer diaeresis spine (longer than outer angle versus shorter). With regards to the form of rostrum, in Thailand, M. tratense is most similar to M. sintangense . But it can easily be distinguished from M. sintangense by the second pereiopods which are smooth and have no velvety setae or tubercles on the fingers (versus covered by spinules on whole leg, with velvety setae on basal half of the fingers and with tubercles on the inner margin of the fingers); the less prominent median processes on the first two abdominal sternites (cf. figure 4E with 2D), and the larger uropodal diaeresis spine (longer than outer angle versus shorter).