The fine morphology of the osphradial sense organs of the mollusca. II. Allogastropoda (Architectonicidae, Pyramidellidae)

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.