Integrative systematics of northern and A rctic nudibranchs of the genus D endronotus ( M ollusca, G astropoda), with descriptions of three new species

The taxonomy of common northern nudibranch molluscs of the genus D endronotus in the vast cold regions of E urasia remains largely unknown. Abundant material collected in many localities from the B arents S ea, via the A rctic region, to the north‐west P acific was analysed for the first time. An integrated approach combining morphological and ontogenetic data with molecular four‐gene ( COI , 16S , H3 , and 28S ) analysis reveals seven species, including three previously undescribed. D endronotus frondosus ( A scanius, 1774) and D endronotus dalli Bergh, 1879 were commonly considered as amphiboreal species; however, according to this study they are restricted to the N orth A tlantic and the N orth P acific, respectively. In the north‐west P acific two new species were discovered, Dendronotus kamchaticus  sp. nov. and Dendronotus kalikal  sp. nov. , that are externally similar to D . frondosus , but that show significant distance according to molecular analysis and are considerably different in radular morphology. In the N orth A tlantic a new species Dendronotus niveus  sp. nov. , sibling to N orth P acific D . dalli , is revealed. The separate status of N orth A tlantic D endronotus lacteus ( T hompson, 1840) is confirmed, including considerable range extension. The essential similarity of early ontogenetic stages of radular development common for species with disparate adult radular morphology (such as D . frondosus and D . dalli ) is shown, and its importance for taxonomy is discussed. © 2015 The Linnean Society of London