Two species of the alpheid shrimp genus Leptalpheus Williams, 1965 are reported from the southwestern Caribbean Sea. Leptalpheus pierrenoeli n. sp. is described on the basis of a single male specimen collected from a burrow of unknown, presumably callianassid host on Isla Grande, Panama. This species differs from all other species of Leptalpheus by the dentition on the fingers of the major cheliped and the elongate stylocerite. Leptalpheus cf. forceps is recorded for the first time from Cahuita, Costa Rica, representing a considerable range extension of L. forceps Williams, 1965, previously known from North Carolina to the Gulf of Mexico, into the southern Caribbean Sea. The Cahuita specimens bear a peculiar segmented filament on the uropodal endopod (caudal filament), a feature not observed in the type specimens. Furthermore, they were found in association with the callianassid ghostshrimp, Lepidophthalmus richardi Felder & Manning, 1997. This finding represents a new host record for L. forceps and a significant range extension of L. richardi, previously known only from the type locality in Belize.
Crustacea, Decapoda, Alpheidae, Leptalpheus, Callianassidae, Lepidophthalmus, Caribbean, western Atlantic infaunal shrimp, burrow, commensalism, new species.