Hidden beauty of the north: a description of Eubranchus scintillans sp.n. (Gastropoda: Nudibranchia) from the Barents Sea and North-East Atlantic

: This paper represents results of an integrative analysis of specimens identified as Eubranchus exiguus (Alder et Hancock, 1848), a common nudibranch species inhabiting hydroid colonies in Northeast Atlantic marine communities. Our study included a molecular analysis, based on mitochondrial COI and 16S rRNA and nuclear histone H3 and 18S rRNA molecular markers. Phylogenetic relationships among species of Eubran-chus Forbes, 1838 were estimated by phylogenetic reconstruction using two algorithms — Bayesian inference and maximum likelihood approaches. The phylogenetic hypotheses were accompanied by species delimitation methods: Assemble Species by Automatic Partitioning (ASAP), Bayesian implementation of the Poisson Tree Processes (bPTP) and General Mixed Yule Coalescent (GMYC). We used COI data to reconstruct a haplotype network for population structure analysis. Morphological defining features were analyzed with a light microscopy and scanning electron microscopy (SEM). Colouration and external appearance of specimens were studied with photographs. Results of the integrative approach indicated the existence of a pseudocryptic new species described herein under the name Eubranchus scintillans sp.n. This new species was found sympatrically with E. exiguus in all studied regions (the Barents and the North Seas).