Architectonicidae

Abstract: The fine structure of the osphradia of Architectonicidae and Pyramidellidae is described. In contrast to their different external shape, the sensory epithelium of the osphradium of both families is very similar, but entirely different from that of all true prosobranchs. There are, however, similarities with the osphradia of basal Opisthobranchia (Bullomorpha). Based on these osphradial characters and supported by several additional anatomical characters, the systematic position of both families is regarded as outside the Prosobranchia, but representing the common basal niveau for Opisthobranchia and Pulmonata.

Abstract: Fifteen species of Heterostropha are described, 12 of them for the first time. All are newly interpreted with regard to their taxonomic relation to fossil and living gastropods. The Streptacidoidea with long Paleozoic history are represented in the Late Triassic St. Cassian Formation by several genera that can be differentiated into four families. The Ebalidae are represented byEbala, with smooth protoconch, Cassianebalidae byCassianebala andLoxebala with axially ornamented protoconch. The Donaldinidae of St. Cassian are represented by one species ofDonaldina and two ofNeodonaldina that stand in the continuation of Paleozoic species ofDonaldina. Architectonicoidea with shells coiled in a plane and Valvatoidea appear in the St. Cassian fauna without known Paleozoic relation. In the former superfamily the Architectonicidae can be recognized in the genusRinaldoconchus with two species. Cassianaxidae withCassianaxis, Amphitomariidae withAmphitomaria, Stuoraxidae withStuoraxis andAmpezzogyra have a sinistral protoconch and planispirally coiled dextral teleconchs. They all resemble different modern species that have similarly small shells. Modern Hyalogyrinidae have withAlexogyra a new representative from the Triassic. The Valvatoidea are represented with the generaCarboninia andBandellina of the Cornirostridae in the Triassic representatives. The relation of described species in the system of the Heterostropha is discussed.

Abstract: The anatomy of the Architectonicidae is described. The family combines prosobranch and pentaganglionate (=euthyneuran) traits, but has evolved in a very specialized way as cnidaria-feeders. There is no close relationship to the Epitoniidae, and the taxon ‘Heterogastropoda’ is regarded as artificial. The closest relatives of the Architectonicidae are the Mathildidae and the Pyramidellidae, all united in a taxon Allogastropoda. This taxon is regarded as a connecting link between basal marine Caenogastropoda and the most primitive Pentaganglionata (e.g. Acteon, Ringicula). The relationships of the Architectonicidae to the Rissoellidae and Omalogyridae are briefly discussed.