Description of Synalpheus williamsi, a new species of sponge-dwelling shrimp (Crustacea : Decapoda : Alpheidae), with remarks on its first larval stage

A new species of Synalpheus is described based on specimens collected from sponges in Belize and the Atlantic coast of Panama. The new species, S. wil liamsi, is most similar morphologically to S. goodei Coutiere, but the two species are consistently different in several morphological and larval feat ures, and occupy distinct species of sponges. The shape of the major chela and of the uropodal exopods are the most reliable morphological characters that distinguish the two species. The first larval stage, a zoea I, was obt ained from an ovigerous female of the new species. The zoea I is similar to that of S. neomeris (De Man), S. triunguiculatus (Paulson), S. tumidomanus (Paulson), and S. scaphoceris Coutiere, in lacking pleopods and chelae, bu t can be distinguished by the presence of an acute projection on the pteryg ostomian corner.