Systematic revision of the speciose sea slug genus Doto (Heterobranchia: Nudibranchia) − from the Mediterranean to South America

Abstract

The genus Doto Oken, 1815 is, taxonomically, one of the most complex genera of nudibranchs due to the cryptic nature of its species, their small body size, and the homogeneity among their internal and external features. Here, an extensive molecular analysis of Mediterranean, Northeastern Atlantic, and South American specimens sheds light on the species-level taxonomy of the group. Our multilocus analyses include 171 specimens, 59 of which are newly sequenced, corresponding to 20 species. Ten species are included in a molecular phylogeny for the first time, two being new species. Here, we provide detailed morphological and ecological descriptions of three Atlantic species, 11 Mediterranean species, and one from the Pacific, complemented by live photographs evidencing their chromatic variation. The phylogenetic and species delimitation analyses suggest that coloration and external morphology are often unreliable for differentiating among species. Molecular evidence corroborates and expands the geographical distribution of Doto species, some of which have never been included in molecular studies. The Mediterranean species currently recognized as D. coronata (Gmelin, 1791) and D. dunnei Lemche, 1976 correspond to D. millbayana Lemche, 1976. Consequently, we suggest the junior synonymy with D. dunnei syn. nov. Nevertheless, we found evidence for a restricted distribution of D. coronata in the western Mediterranean, coexisting in sympatry with D. cavernicola sp. nov. An additional new species from the Chilean Patagonia is also described as D. vrenifossorum sp. nov. Considering the present phylogenetic scenario, there is a highlighted need for further new morphological and genetic evidence, expanding the number of taxa and species to further unravel the taxonomy of Doto.