Biodiversity hotspot in cold waters: a review of the genus Cuthonella with descriptions of seven new species (Mollusca, Nudibranchia)

Cuthonella Bergh, 1884 is of one of the most neglected nudibranch groups, with a long history of
taxonomic confusion with other aeolidacean genera. Owing to its predominantly Arctic distribution with cold water, its species are difficult to find and to collect, and thus to describe. In this study we revise the
genus by presenting molecular and morphological data for a majority of the species, including the type,
C. abyssicola Bergh, 1884. The material is based on a broad geographic sampling throughout the Northern
Hemisphere. Particular emphasis is placed on the Kuril Islands, a diversity hotspot for the genus. Seven
new species and two subspecies of Cuthonella are described from the Arctic and North Pacific regions. The
number of species of Cuthonella is thus increased over threefold and now comprises 15 species plus two
subspecies instead of five species. This work is the most substantial update of the genus Cuthonella since
its description in 1884. To delineate taxonomic and phylogenetic limits of Cuthonella-like aeolidaceans,
the molecular phylogeny of the wider traditional “tergipedids” is presented and shows that Cuthonellalike
aeolidaceans form a distinct molecular clade as the family Cuthonellidae Miller, 1977, corroborated
by reliable morphological apomorphies.