Young but distinct: description of <i>Eubranchus malakhovi </i>sp.n. a new, recently diverged nudibranch species (Gastropoda: Heterobranchia) from the Sea of Japan
In this paper we perform an integrative investigation of the Eubranchus odhneri - Eubranchus sanjuanensis species complex. Several specimens morphologically similar to E. sanjuanensis were collected in the Sea of Japan. However, preliminary molecular data indicated that they were closer to the Arctic species E. odhneri . For our analysis we obtained new data on mitochondrial COI and 16S rRNA, and nuclear histone H3 and 18S rRNA molecular markers to reconstruct their phylogeny (Bayesian Inference and Maximum Likelihood approaches), delimit species with ASAP, bPTP and GMYC analyses and estimate divergence times of putative species. We also studied morphological and ecological features including external morphology, colouration, jaw and radular morphology, configuration of the reproductive system, ultrastructure of cnidosacs, and determination of possible diet preferences. Our results show that specimens from the Sea of Japan represent a new species described herein, Eubranchus malakhovi sp.n. It differs both morphologically and genetically from its closely related species, the Arctic E. odhneri and the North-East Pacific E. sanjuanensis . The new species is closely related to E. odhneri with low mtDNA divergence, and our divergence time estimations suggest these species split ~1.5 Mya.