3D reconstruction of the anatomy of the ovoviviparous (?) freshwater gastropod Borysthenia naticina (Menke, 1845) (Ectobranchia: Valvatidae)

摘要

Because of its apertural shape and an unusual reproductive mode, Borysthenia naticina ( Menke, 1845) has always held a special position within the Valvatidae. The species is known to be viviparous, whereas all other valvatids produce spawn. Living animals from the Bavarian Danube river provided the opportunity to investigate the structure of the genital system in relation to this special mode of reproduction. We applied 3D surface- and volume-rendering techniques using AMIRA, based on histological semithin slices. We also provide SEM photos of the taenioglossate radula of this species. Contrary to our expectations, there were no special structures (e.g. brood pouch) in the genital system that could be connected with such an accelerated early ontogeny. In general, only minor anatomical differences were found between Borysthenia naticina and other valvatid species. The previous reports of ovoviviparity need at least to be modified, because true spawn was observed, although the embryos were close to hatching. The generally accepted taxonomic status of Borysthenia as a genus distinct from Valvata is doubtful, and the family Valvatidae is in need of a thorough systematic revision.