A NEW SPECIES OF RIMICARIS (CRUSTACEA, DECAPODA, BRESILIIDAE) FROM THE SNAKE PIT HYDROTHERMAL VENT FIELD ON THE MID-ATLANTIC RIDGE

A second species of the bresiliid shrimp genus Rimicaris Williams & Ro na, 1986, R. aurantiaca, is described from the Snake Pit hydrothermal vent field on the Mid-Atlantic Ridge. The species possesses a highly u nusual dorsal light receptive organ (the ''dorsal eye'') beneath the c arapace, as does R. exoculata Williams & Rona, 1986, but is considerab ly smaller than that species and in many ways bridges the morphologica l gap between the genera Rimicaris (previously monotypic) and the genu s Chorocaris Martin & Hessler, 1990. Characters in common with R. exoc ulata include the presence of the dorsal eye, lack of a well developed carpal cleaning brush on the cheliped, smooth (not notched) lateral b order of the antennal scale, and brush-like pad of setae on the dactyl us of the second maxilliped. Characters in common with species of Chor ocaris include the relatively normal (not inflated) carapace, slightly produced rostrum, presence of recognizable eyestalks, and absence of a carapacial notch at the base of the antennal area that forms, with t he carapace, an opercular shield such as is seen in R. exoculata. Prev ious descriptions of the dorsal eye of R. exoculata show that it diffe rs from the dorsal eye of R. aurantiaca. The new species is also chara cterized by the presence of large numbers of orange-colored oil drople ts visible through the dorsum of the carapace and through the thin cut icle of the abdominal sternites and, to a lesser degree, through the c uticle of the abdominal terga. The definition of Rimicaris is revised to accommodate the new species.