Description and phylogeny of Isaacsicalanus paucisetus , n. gen., n.sp., (Copepoda: Calanoida: Spinocalanidae) from an East Pacific hydrothermal vent site (21 degree E)

A new genus and species of Spinocalanidae is described under the name Isaacsicalanus paucisetus . It was collected adjacent to the seafloor of the East Pacific Rise off the mouth of the Gulf of California. The copepod was observed swimming in a small swarm, apparently unispecific and all adult females, among concentrations of macrobenthic invertebrates typical of known hydrothermal vent communities. The new copepod's most distinctive morphological features relative to other spinocalanids are the longer urosome, shorter antennule, and fewer setae on oral appendages. Phylogenetic analysis supports the hypotheses that the new genus occupies a highly derived position within the Spinocalanidae and that the family is the most primitive within the superfamily Clausocalanoidea.