3D-microanatomy and histology of the hydrothermal vent gastropod Lurifax vitreus Warén & Bouchet, 2001 (Heterobranchia: Orbitestellidae) and comparisons with Ectobranchia

Abstract

Up to now, the internal anatomy of representatives of only two of three recent genera of the Orbitestellidae have been described. Herein, a species of the third genus, Lurifax vitreus from hydrothermal vent sites of the North Atlantic, is examined on the basis of semi-thin sections. Data on three-dimensional (3D)-anatomy and histology are provided in order to increase knowledge of the family. In addition, the original serial sections of Orbitestella wareni and Microdiscula cf. subcanaliculata of the original paper by Ponder (Journal of Molluscan Studies 56:515–532, 1990a) were reinvestigated and compared with Lurifax vitreus. Although Lurifax vitreus is significantly larger than the two former genera, it is again devoid of a gill but shows opponent ciliary stripes and a pallial tentacle. Most orbitestellid characters reflect plesiomorphic conditions among the Heterobranchia; autapomorphies of the family include an orthostrophic protoconch, massive jaws, a diagnostic radula type, paired posterior pedal glands with a common opening, and a pedally innervated copulatory organ. In agreement with actual molecular trees, our data suggest a placement of Orbitestellidae as basic Heterobranchia outside of Ectobranchia (Valvatoidea).