Yamaguchi, ToshiyukiNewman, William A.2008-04-182008-04-181990-04Yamaguchi T, Newman WA. 1990. A new and primitive barnacle (Cirripedia: Balanomorpha) from the north Fiji Basin abyssal hydrothermal field, and its evolutionary implications. Pac Sci 44(2): 135-155.0030-8870http://hdl.handle.net/10125/1266A new sessile barnacle, Eochionelasmus ohtai, n. gen., n. sp., has been discovered associated with an abyssal hydrothermal vent at 1990m depth in the North Fiji Basin, Southwest Pacific. The genus is distinguished from its closest and bathyal relative, Chionelasmus, in having distinct, multiple whorls of basal imbricating plates. These and other characters render it the most primitive living member of the suborder Balanomorpha. Knowledge of the organization of its shell, and of the ontogeny of the shell wall in Chionelasmus, profoundly alters our understanding of the evolution of balanomorph barnacles, and a new hypothesis is proposed. Two previously described abyssal hydrothermal barnacles also proved to represent the most primitive living members of their suborder s: Scalpellomorpha and Verrucomorpha. It may be puzzling why three such antiquated morphologies should have persisted in association with abyssal hydrothermal springs while their antecedents became extinct elsewhere. However, barnacles are noted f(or their adaptability to a wide range of habitats including rigorous environments such as estuaries, the highest intertidal, and the effluent from power plants. The notable feature here, in contrast to their conservative but distinctly different shell morphologies, is the uniquely convergent adaptation of their setose feeding mechanism to vent-related food sources.en-USArticle