A new genus and species of the family Anulidentaliidae (Scaphopoda: Dentaliida) and its systematic implications

Abstract

Shell, radula, and anatomy of Epirhabdoides ivanovi new genus and species are described from a sample of the Russian Vitjaz Expedition from the Japan Trench. It is distinguished from the similar Laevidentalium sominium by shell morphometrics and radula morphology. The radula is almost identical with that of Anulidentalium bambusa (Anulidentaliidae). The anatomy of the mantle margins, however, including dorsolateral slits at the anterior mantle margin and a connective tissue bolster at the posterior mantle opening is that of the family Rhabdidae. In a parsimony analysis Epirhabdoides ivanovi takes an intermediate position between a basal grade of Gadilinidae and the remaining Dentaliida implying convergent evolution of mantle characters. An alternative but less parsimonious tree with E. ivanovi as sister taxon to Rhabdus requires convergences in radula characters. This is the first documented case of convergent anatomical features among Scaphopoda and enhances the need of radula and soft part investigation of the conchologically little informative, smooth-shelled dentaliid groups.