Macrobrachium dolatum, 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 : 598-604

Macrobrachium dolatum sp. nov.

(figures 6, 7)

Material examined

H: W, cl 22.5 mm ( ZRC 2000.2644 ), Trang, South Thailand, 29 October 1988 .

P: 1 W, cl 20 mm (CU 1997.105), same data as holotype.

Description

Rostrum (figure 7A) reaching to or slightly beyond end of scaphocerite, dorsal margin sinuous, 0.65 times as long as carapace length, dorsal margin of rostrum with 13 teeth, ventral with four teeth, three dorsal teeth behind postorbital margin, occupying about one-third length of carapace, postorbital teeth more widely spaced than others. Antennal spine sharp, situated slightly below inferior orbital angle. Hepatic spine smaller than antennal spine, lying behind and slightly below antennal spine. Carapace with fine spinules.

Third thoracic sternite with indistinct transverse ridge, fourth thoracic sternite with prominent median process (figure 7D). Abdomen (figure 6A) smooth, glabrous, first to third pleurites broadly rounded, fourth and fifth feebly posteriorly produced, fourth and fifth subtriangular, sixth abdominal somite 1.3 times as long as fifth, posterolateral angle strongly produced, acute, posteroventral angle feebly produced, subacute. Telson (figure 7F) 1.8 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 sternites (figure 7E), that of second abdominal sternite larger, pointed, that of third indistinct. 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 7B) 2.8 times as long as broad, with straight outer margin.

Epistome as in figure 7C, bilobed by a deep depression.

Mouth parts as in figure 6. Mandibular palp slender, three-segmented; incisor process robust (figure 6C); metastoma with paragnathus (figure 6B) proximally fused forming a broad corpus with well-developed anterior median depression, paragnaths distally bilobed, upper lobe large, elliptical. Maxillular (figure 6D) palp bilobed, upper lobe slender, lower lobe stout; maxilla (figure 6E) with simple palp, basal endite deeply bilobed, scaphognathite normal; first maxilliped (figure 6F) with setose palp, basal and coxal endites distinct, flagellum of exopod with numerous plumose setae distally, epipod deeply bilobed; second maxilliped (figure 6G) with normal endopod, flagellum with numerous plumose setae distally, epipod simple, with welldeveloped podobranch; third maxilliped (figure 6H) with robust endopod, exopod with numerous plumose setae distally, reaching to distal margin of ischiomerus.

First pereiopod (figure 7G) slender, reaching beyond scaphocerite by entire chela, equal in length, similar in form. Palm as long as fingers, carpus 2.2 times as long as chela, merus shorter than carpus. Male second pereiopods (figure 7H) equal in length, similar in form. Second pereiopod reaching beyond scaphocerite by onequarter of merus, distinctly longer than total length. Fingers (figure 7I) covered by dense velvety pubescence on proximal two-thirds of length; both fingers curved inwards, with tips crossing when fingers closed, small gaping, one large tooth at proximal sixth of fixed finger, two large teeth at proximal one-quarter of movable finger, tooth at fixed finger larger than those of movable finger, fitting into gap between smaller teeth of movable finger when closed; cutting edge of distal onethird of the fixed finger with razor-like edge; cutting edge of movable finger with two small granules; fingers slightly shorter than palm. Palm cylindrical, 6.0 times as long as broad. Carpus distinctly shorter than chela, longer than palm. Merus slightly shorter than palm. Last three pereiopods slender, similar in form. Third pereiopod (figure 7J, K) reaching beyond scaphocerite by one-quarter of carpus. Dactylus short but slender, 5.8 times as long as broad. Propodus 3.1 times as long as dactylus, with about 10 spinules on posterior margin. Fifth pereiopod more slender than third one, with entire dactylus reaching beyond end of scaphocerite.

Endopod of male first pleopod reaching half of exopod, 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 (figure 7L), shorter than outer angle.

Etymology

The name of the species is adopted from the Latin, dolo, for cut and hew, alluding to the razor-like cutting edge of the fixed finger.

Habitat Unknown.

Remarks

Macrobrachium dolatum sp. nov. resembles M. sintangense (De Man, 1898) . However, it can be distinguished from M. sintangense by the form of the rostrum, which is sinuous along the dorsal margin (straight in M. sintangense ); the distinct and sharp median process on the fourth thoracic sternite and the first two abdominal sternites (figure 7D, E versus figure 2C, D); the stouter second pereiopod (figure 7H versus figure 2H); the cutting edge of the distal one-third of the fixed finger with razor-like edge (versus cutting edge not razor-like in M. sintangense ); and the relatively shorter spine at the uropodal diaeresis (shorter than outer angle versus longer or as long as in M. sintangense ).