Biogeographic patterns of distribution of the mollusc Zelentia ninel (Nudibranchia, Trinchesiidae)

In the present contribution we report, for the first time, records of the nudibranch Zelentia ninel from Norway. The species is previously known only from the Barents Sea coast in northern Russia where it was described for the first time in 2017. Records of Z. ninel from six different localities in northern Norway from 2019-2023 are presented and discussed. The identity of the specimens was determined by investigation of external and internal morphology as well as molecular analysis of preserved specimens. Photographs of live specimens and radulae of preserved specimens are presented, and species delimitation is confirmed by molecular phylogenetic analysis. In order to assess the biogeographic distribution of Z. ninel based on all available information, recent unanticipated genetic data supporting a putative occurrence of Z. ninel at the Aleutian Islands, Alaska is also discussed where we provide arguments in support of occasional anthropogenic transportation outside its natural range. The present records significantly expand the known natural range of distribution for Z. ninel and demonstrate that the species is not restricted to the Russian Barents Sea coast but that the range encompasses also at least northern Norway. These data can provide important insights to the understanding of natural ranges of marine invertebrates across biogeographical regions affected by rapid ongoing climatic change.