Assessing the systematics of Tylodinidae in the Mediterranean Sea and Eastern Atlantic Ocean: resurrecting Tylodina rafinesquii Philippi, 1836 (Heterobranchia: Umbraculida)

ABSTRACT

The systematics of the gastropod clade Umbraculida, particularly the family Tylodinidae, has been a matter of debate. The Tylodinidae of the Mediterranean Sea are a case in point, with no comprehensive molecular assessment of diversity having been carried out to date. Several species and genera have been erected and synonymized in the course of the last two centuries and only a single species from each of the genera Tylodina and Anidolyta are considered to be present in these waters. In order to shed light on the controversial taxonomy of the group, we carried out both morpho-anatomical study and molecular analyses using fragments of two mitochondrial genes, cytochrome c oxidase subunit I and 16S rRNA, and the nuclear gene histone H3. Phylogenetic analyses and species delimitation tests clearly recovered two independent lineages of Tylodina from the Mediterranean and Eastern Atlantic coast, the type species T. perversa and the resurrected T. rafinesquii. We found clear differences in shell and radular morphology between both species, as well as differences in their habitat and food preferences. Interestingly, we found strong evidence that T. rafinesquii is sister to T. fungina from the Eastern Pacific rather than to the sympatric T. perversa. Furthermore, the new morphological data strongly encourage the suppression of the genus Anidolyta, which should be considered a junior synonym of Tylodina.