PROC. BIOL. SOC. WASH. 96(4), 1983, pp. 725-757 A REVISION OF THE SEGUENZIACEA VERRILL, 1884 (GASTROPODA: PROSOBRANCHIA). I. SUMMARY AND EVALUATION OF THE SUPERFAMILY James F. Quinn, Jr. Abstract.— A summary of the superfamily Seguenziacea is compiled from the Hterature and unpubUshed observations, and a complete bibliography is presented. A taxonomic resume of seguenziacean genera is given. A preliminary classification of the superfamily includes 74 nominal species and subspecies in seven genera and four species-groups within Seguenzia. The known characters of the shells and anatomy are reviewed. The superfamily Seguenziacea is shown to be distinct from any other known archaeogastropod or mesogastropod superfamily. This super-family is characterized by: nacreous shells of archaeogastropod ultrastructure, often complexly sculptured with 0-3 (usually 2 or 3) labral sinuses; modified rhipidoglossate radula (formula 1 2-4. 1.1.1.4-12); paucispiral corneous operculum; epipodial tentacles; monopectinate ctenidium; long intestine with an anterior loop; specialized structures in the reproductive tract (e.g., a well developed penis); and modification of the mantle edge to form distinct incurrent and excurrent siphons. Contents of the intestine of Seguenzia sp. cf S. eritima Verrill indicate that Seguenzia is a detritivore. Ancistrobasis is known from the Eocene, Pliocene, and Recent; Seguenzia occurs from the Miocene to the Recent; all other genera are unknown as fossils. Although probably derived from the Trochacea, no direct link with any known fossil or living prosobranch group has yet been established. The superfamily Seguenziacea is here considered to be an isolated offshoot of the Trochacea, independently acquiring advanced anatomical features of a mesogastropod nature as a conse-quence of extremely small body size and in response to a deep-water habitat. The enigmatic superfamily Seguenziacea comprises a group of very small (usu-ally 5 mm or less in height), trochoid-like prosobranchs of world-wide distribution. Although a few species have been recorded from outer continental shelf or abyssal plain depths, by far the majority of known species have been described from the continental slopes. Because of their deep-water habitats, information concerning seguenziacean species has been largely confined to original species descriptions and records published in reports of major national exploratory expeditions. Very few species are represented in collections by large series of specimens, and even fewer have been collected alive. As a result, the taxonomy and systematic position of the Seguenziacea have remained in states of confusion and debate. As a first step towards resolving the status and relationships of this group, a review of all information in the literature is presented, augmented by original observations. The observations summarized here suggest that seguenziaceans are archaeo-gastropods which have acquired anatomical specializations more typical of a mesogastropod organization. Archaeogastropod affinity is indicated by the na-creous shell, protoconch, epipodial tentacles, anterior loop of the intestine, and
BioStor
