Functional morphology of the gonoduct of the gastropod Bulla striata Bruguière, 1792 (Opisthobranchia: Cephalaspidea): evidence for a monaulic system

Reproductive systems are a major source of characters for systematics and phylogenetic inference in the Gastropoda and therefore knowledge of their morphology, homology and function is important. In the cephalaspidean genus Bulla the reproductive system is hermaphroditic and is divided into ovotestis, posterior gonoduct, anterior female glands and copulatory organs. Previous accounts failed to explain fully the organization and function of this complex system. We use a new approach based on fine dissection, gross serial cross-sections and scanning electron microscopy to study the female glands of the European species Bulla striata . We provide a re-description of the gonoduct and infer possible pathways of gametes and location of processes. Based on the absence of separate ducts or grooves for ova and spermatozoa, we conclude that Bulla is a monaulic cephalaspidean.