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. williamsi, is most similar morphologically to S. goodei Coutiere, but the two species are consistently different in several morphological and larval features, 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 obtained 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, but can be distinguished by the presence of an acute projection on the pterygostomian corner. Resumen. —Se describe una nueva especie de Synalpheus en base a especfmenes recolectados dentro de esponjas en Belice y la costa Atlantica de Panama. La nueva especie, Synalpheus williamsi, es muy parecida a S. goodei Coutiere, pero posee distintas caracterfsticas ecologicas, morfologicas y larvarias. Estas dos especies de Synalpheus habitan distintas especies de esponjas. Los caracteres morfologicos m£s confiables para distinguirlas son la forma de la quela mayor y de los exopodos uropodales. De una hembra ovfgera se obtuvo la primera fase larvaria, una zoea I desprovista de pleopodos y de quelas. La zoea I de la nueva especie es muy similar a la de S. neomeris (De Man), S. triunguiculatus (Paulson), S. tumidomanus (Paulson), y S. scaphoceris Coutiere, pero se distingue de ellas por la presencia de una proyeccion pterigostomiana aguda en el caparazon. During the course of collections made over several years in Belize and on the Atlantic coast of Panama, we obtained a number of shrimps of a sponge-dwelling Synalpheus species morphologically similar to S. goodei Coutiere, 1909. Specimens were collected from living sponges taken by SCUBA from various depths (1-15 m) on the outer reef ridge at the Smithsonian Institution's field station on Carrie Bow Cay, Belize (16°48'N, 88°05'W), and from Ulagsukun, Pico Feo, and Mamitupo reefs near the Smithsonian Tropical Research Institute's (STRI) field station in the San Bias Islands, on the Atlantic coast of Panama (9°34'N, 78°58'W). Specimens from both areas were collected from the internal canals of the midnight-blue sponge Hymeniacidon caerulea Pulitzer-Finali, 1986, although one was associated with an unidentified orange encrusting sponge of tubular shape. Four specimens were collected free from any host, and had probably left their host sponges during sample handling. Usually, a heterosexual pair or a single adult was found in a same sponge. Here we deVOLUME 112, NUMBER 3 543 Fig. 1. Synalpheus williamsi, new species. Paratype male 4.4 mm (USNM 276160): a, anterior region of carapace and cephalic appendages, dorsal view; b, same, lateral view; c, telson and uropods, dorsal view. Paratype ovigerous female 4.3 mm (USNM 276160): d, anterior region of carapace and cephalic appendages, dorsal view; e, anterior region of carapace, lateroventral view. Scale bar = 1 mm for a, b, d, e and 0.72 mm