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

The first sessile barnacle from a deep-sea hydrothermal vent of the Ea st Pacific Rise (EPR) has been recovered by the French submersible Nau tile from 17 degrees 25'S, north of Easter Island. It is similar in ge neral appearance to the most primitive living balanomorph barnacle Eoc hionelasmus 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 dist inct. Therefore, it is recognized here as a new species of the previou sly monotypic genus Eochionelasmus. However, it is anticipated that ev en greater differences will be found between the two species when full y developed individuals of the Easter Island form are found. If so, di stinction 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 t he East Pacific Rise, but it is also the first from a midocean ridge. This discovery corroborates the hypothesis that biotic exchange betwee n midocean ridges and backarc basins occurs relatively infrequently or was curtailed a long time ago.