Was Gordon Robilliard right? Integrative systematics suggest that Dendronotus diversicolor (multicolor frond-aeolis) is a valid species

Abstract

Nudibranch molluscs of the genus Dendronotus Alder and Hancock, 1845 are widely distributed in the Northern Hemisphere. Taxonomic studies on the genus Dendronotus have been problematic due to high variability in the colour pattern of many species, as well as in the external morphology and anatomy. In the present paper, we studied specimens of Dendronotus from northern Pacific presumably belonging to the species Dendronotus albus MacFarland, 1966 (white frond-aeolis). Molecular and morphological data revealed the existence of two distinct species among the material examined: D. albus, which has a wide range from Kamchatka and the Kurile Islands (from where we report this species for the first time) to California in North America, and the pseudocryptic species Dendronotus diversicolor Robilliard, 1970 (multicolor frond-aeolis), which has been previously considered a junior synonym of D. albus. Dendronotus diversicolor occurs from California, USA, to British Columbia, Canada, in sympatry with D. albus. Dendronotus albus and D. diversicolor can be clearly distinguished by colour pattern, internal and external morphology, and molecular sequence data. Despite some similarities in radular and external morphology between D. albus and D. diversicolor, these two species are phylogenetically distant and belong to different clades within the genus Dendronotus, which suggests convergent evolution.