The taxonomy of the Didemnidae (Ascidiacea) of the central Pacific, including Indo-Pacific records

Abstract

The Ascidlacea--phylum Chordata, sUbphylum Tunicata--as a larva has a notochord and a dorsal nerve cord; as an adult, pharyngeal gl I I slits. Unlike the mature Thaliacea and Larvacea of the Tunicata, the ad~lt ascidian is sessile. Members of the family Didemnidae are distinguished from all other colonial ascidians, which also bud as weI I as reproduce sexually, by pyloric budding and by the frequent occurrence of stellate calcareous spicules. Little taxonomic work has been carried out on Pacific Ocean didemnid ascidians except in marginal areas. Didemnids are abundant coral-reef animals and in some areas are the only ascldians found. The purpose of the present study is to examine various didemnid fauna of the central Pacific area in an attempt to clarify the taxonomic position of these members of the fami Iy Didemnidae. The bases for generic and specific determinations are re-evaluated, an extensive collection of specimens is identified, and pertinent taxonomic problems are clarified and, occasionally, resolved.