Leptalpheus felderi n. sp., a commensal alpheid shrimp, is described from two localities in the southern Caribbean Sea: Isla Margarita, Venezuela and Bahía Cispata, Colombia. All specimens of L. felderi n. sp. were collected with the aid of a suction pump; the Venezuelan specimens came from burrows of the upogebiid mudshrimp Upogebia omissa Gomes Corrêa, 1968. The new species is unique among species of Leptalpheus Williams, 1965 in having small triangular crests on the orbital hoods; a dense row of long, flexible setae on the dactylus of the major chela; two subacute distal processes on the carpus of the major chela; minute, saw-like teeth on the pollex of the minor chela; and only four instead of the usual five segments in the carpus of the second pereiopod. The new species is also characterized by the pinkish-red colour. The diagnosis of the genus Leptalpheus is significantly emended, to accommodate L. felderi n. sp. The taxonomy and intra-generic relationships of Leptalpheus species are discussed, and a table of all species of Leptalpheus, with information on the distribution and hosts, is provided. Because of the invalid description, L. petronii Ramos-Porto & Souza, 1994 is placed in synonymy of L. axianassae Dworschak & Coelho, 1999. Three preliminary species groups, based mainly on the features of the major cheliped and frontal region, are established.
Alpheidae, Leptalpheus, Upogebia, commensal shrimp, infauna, western Atlantic, genus emendation, new species.