Species identity and genetic structure of nemerteans of the “Lineus ruber–viridis” complex (Muller, 1774) from Arctic waters

Lineus species are the most abundant nemerteans that inhabit boreal regions of the Atlantic and Arctic Oceans and are the focus of many zoological studies. However, its taxonomy and species composition in Arctic areas remain poorly known. In this study, we performed an updated genetic analysis of nemerteans from the “Lineus ruber–viridis” complex, clarified its species composition in the White Sea, and identified their diagnostic features. Molecular data based on mtDNA analysis indicate the presence of L. ruber, L. viridis, and L. clandestinus in the studied area, which was consistent with morphological data. Short descriptions of external morphological features are provided. External morphologies of European and White Sea Lineus species have some peculiarities: L. clandestinus from the White Sea lacks the iridescent ventral fold, and L. ruber has an unusual “green” form. The recovered genetic structure differed among the three species, which may have resulted from different dispersal scenarios during the last glacial maximum. The low level of nucleotide diversity combined with the typical star-like structure of the network indicated that an ancestral northern L. ruber population underwent a bottleneck event in the recent historical past.