EOCHIONELASMUS PAQUENSIS, NEW SPECIES (CIRRIPEDIA: BALANOMORPHA), FROM 17?25'S, NORTH OF EASTER ISLAND: FIRST RECORD OF A SESSILE HYDROTHERMAL BARNACLE FROM THE EAST PACIFIC RISE

Abstract

ABSTRACT The first sessile barnacle from a deep-sea hydrothermal vent of the East Pacific Rise (EPR) has been recovered by the French submersible Nautile from 17°25'S, north of Easter Island. It is similar in general appearance to the most primitive living balanomorph barnacle Eochionelasmus ohtai known from the North Fiji, Lau, and Manus Basins, in the Southwest Pacific (Yamaguchi and Newman, 1990; Galkin, 1992), but the morphology of its opercular plates, mouthparts, and cirri is distinct. Therefore, it is recognized here as a new species of the previously monotypic genus Eochionelasmus. However, it is anticipated that even greater differences will be found between the two species when fully developed individuals of the Easter Island form are found. If so, distinction at the genus-group level will need to be evaluated. The new species is not only the first record of a sessile vent barnacle from the East Pacific Rise, but it is also the first from a midocean ridge. This discovery corroborates the hypothesis that biotic exchange between midocean ridges and back-arc basins occurs relatively infrequently or was curtailed a long time ago.