New genus of Aegisthidae (Copepoda : Harpacticoida) from hydrothermal vents on the Galapagos Rift

Both sexes of Andromastax muricatus, new genus, new species (Copepoda: Harp acticoida: Aegisthidae), are described from a hydrothermal vent on the Gala pagos Rift in the eastern Pacific. This epibenthic species represents the m ost primitive aegisthid known to date, displaying several plesiomorphic cha racter states in the cephalosomic appendages and in P5 and P6. The new spec ies shares some characters with the imperfectly described Aegisthus spinulo sus, which is removed from Aegisthus and placed here as a species incertae sedis in the Aegisthidae. The basic setal pattern on the caudal rami in the Aegisthidae is reconsidered and the different degrees of atrophy of the mo uthparts in the nonfeeding males are discussed. It is postulated that the f amily evolved from an epi- or hyperbenthic ancestral stock and that the col onization of the open pelagic environment by Aegisthus is secondary.