Interactive 3D-anatomical reconstruction and affinities of the hot-vent gastropod Xylodiscula analoga Warén & Bouchet, 2001 (Ectobranchia)

The heterobranch family Xylodisculidae Warén, 1992 includes about a dozen described species, the taxonomy of which is mostly based on hard parts (shell, operculum, radula) with occasional reports on the external morphology. By applying semithin sectioning, digital photography and 3D-reconstruction, we describe for the first time the anatomy and histology of a xylodisculid, Xylodiscula analoga Warén & Bouchet, 2001. Described from hot-vent habitats, this species is exceptional among Xylodisculidae for its extraordinary size and atypical taenioglossate-like radula. Anatomy and histology confirm a placement of monophyletic Xylodisculidae among the Heterobranchia: Ectobranchia. Members of the family combine a unique radula type with a plesiomorphic alimentary and genital system; the latter is monaulic, lacks a copulatory organ and possesses a separated receptacle apparatus. Due to lack of data on soft bodies of other xylodisculid species and because molecular data are entirely missing for the family, a robust hypothesis on the systematics of Xylodisculidae cannot yet be provided.