Exploring the intriguing arrival of Vayssierea Risbec, 1928 slugs in the Atlantic Ocean from the Indo-Pacific (Mollusca, Nudibranchia)

Vayssierea is an understudied nudibranch genus characterized by its orange colouration and small size (up to 5 mm in length). To date, there are four described species, distributed in the Indo-Pacific Ocean. Here, individuals of Vayssierea were recorded for the first time in the North Atlantic Ocean on the Canary Islands (Spain). This study aims to evaluate the systematic and taxonomic status and distribution of the genus through multilocus phylogenetic, morphological, and radular analyses. Phylogenetic results show the monophyly of Vayssierea and evidence indicating that the genus is included in the new subfamily Okadaiinae stat. nov. within Polyceridae. According to species delimitation tests, four different species have been sequenced from Russia to Australia, in addition to our new records in the Atlantic Ocean, but more information is needed to identify the species. Nevertheless, our specimens from the Canary Islands belong to two different species, one of which is identical to the Australian species. Bearing in mind that they lack a planktonic larval stage; we hypothesize that they arrived by shipping transportation or aquarium releases, becoming a non-indigenous species of the Atlantic Ocean.