Abstract The heterobranch molluscs of the genus Cylichnoides Minichev, 1977 are widely distributed in boreal and Arctic waters. The present study is the first integrative taxonomical analysis of the genus Cylichnoides combining morphology with molecular phylogenetics (COI, 16S, H3, and 28S). Our goal was to verify the monophyly of traditionally identified species and reconsider morphological diversity in the light of novel molecular data. Traditionally identified species C. validus, C. occultus, C. densistriatus, and C. scalptus are monophyletic, but the latter three species are represented by at least two divergent mitochondrial subclades each (COI, 16S). The morphological analysis does not show differences between these subclades, and no clade-specific divergence was observed in studied nuclear markers as well. We hypothesize that this may be a result of population fragmentation in combination with local extinction and bottleneck events, which is common for widely distributed species. Finally, we demonstrate that specimens of C. scalptus from the Kara Sea represent a derived lineage on the phylogenetic tree, apart from specimens collected from the type locality of this species. Specimens from the Kara Sea also show considerable morphological differences from all other described Cylichnoides species and, therefore, a new species C. karaensis sp. nov. is described herein.
Chaban et al. (Tue,) studied this question.
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