Macrobrachium denticulatum Ostrovski, da Fonseca & da Silva-Ferreira, 1996

Macrobrachium denticulatum Ostrovski, da Fonseca & da Silva-Ferreira, 1996 View in CoL

Macrobrachium denticulatum Ostrovski, da Fonseca & da Silva-Ferreira 1996: 361 View in CoL ;— Ramos-Porto & Coelho 1998: 333;— Melo 2003: 348.

Material Examined. Brazil. Alagoas: 1 male (CL 11.76 mm) DZUFRJ3881 [holotype]: rio São Francisco , 29 Jan. 1995, collector: Matos, F. J. P.; 1 female (CL 11.39 mm) DZUFRJ3880 [paratype]: riacho Marau — tributary of the rio São Francisco , Brazil, 23 May 1992, collector: Ostrovski, F.; 2 males (CL 15.45 mm and 11.58 mm) DZUFRJ3882 [paratypes]: rio São Francisco , 21 May 1992, collector: Matos, F. J. P.; 13 males (CL 7.2–9.97 mm) DZUFRJ2257 [paratypes]: rio São Francisco , Xingó, 29 Jan. 1995, collector: Matos, F. J. P.; 4 males (CL 08.21– 11.20 mm) DZUFRJ2660 : rio São Francisco , 29 Jan. 1995, collector: Matos, F. J. P.

Morphological Characterization. Rostrum almost straight, reaching the distal end of the antennular peduncle, with 13–16 regularly spaced teeth on the upper margin, 5–6 of which are located behind the orbit. A small gap is observed between the 1 st and 2 nd teeth, which are larger than the others. Lower margin bears 1–3 teeth.

Lower portion of orbit is convex and slightly pronounced. Scaphocerite is three times as long as it is wide; epistome bilobed with weakly developed carinae. Carapace smooth with no setae; hepatic spine smaller than antennal spine.

First pair of pereiopods extends to one half to one third of the carpus beyond the scaphocerite. Fingers shorter than palm; carpus twice the propodus length, with merus being two thirds the carpus length, with some variation.

Second pair of pereiopods (P2) significantly unequal in shape and size, with a high incidence of spines; larger pereiopods reached from one half of the merus to one half of the carpus beyond the scaphocerite. Fixed finger has two to five small teeth and one large tooth in the proximal portion of the cutting edge, followed by five to six smaller teeth from the finger to its distal portion. The smaller P2 has fingers forming a gap, cutting edge has two to five small teeth and one large tooth in the proximal part, and longitudinal rows of spinules on the palm and fingers, with the inner ones being larger and more widely spaced. Carpus has the same length as palm and slightly longer than merus. Along the upper margin of the chela, there is a row of teeth with the highest incidence on palm, decreasing in size toward the fingers.

Pleon smooth; pleura of the 5 th somite slightly acute. Internal appendage of second pair of pleopods longer than the male appendage. Preanal carina small and rounded, with or without apex setae.

Posterior margin of telson has a sharp median point with two pairs of posterior cuspidate setae, where the inner cuspidate setae extend beyond the posterior margin of the telson, with many long setae between them.

Sexual dimorphism. Females have a less-developed second pair of pereiopods, which are slightly unequal in shape and size, with a reduced number of teeth. Half of the carpus goes beyond the end of the scaphocerite. The distribution of teeth along the cutting edge is similar to that in males but they are less developed.

Distribution. Endemic species of the São Francisco River, between states of Alagoas and Sergipe, Brazil ( Ostrovski et al. 1996).

Remarks. There are variations in the length relationship between the second pair of pereiopods and the scaphocerite, with one half of the carpus to one half of the merus extending beyond the scaphocerite, and even the distal part of the merus reaching the scaphocerite, diagnostic characters also present in M. olfersii . Another inconsistent diagnostic character when compared to M. olfersii is the number of teeth on the cutting edge of the fixed finger, which varies considerably. The fixed finger may have two to five small teeth and one larger tooth in the proximal portion.