Vol.:(0123456789) 1 3 Polar Biology https://doi.org/10.1007/s00300-018-2438-7 ORIGINAL PAPER Species identity and genetic structure of nemerteans of the “Lineus ruber–viridis” complex (Muller, 1774) from Arctic waters Irina A. Cherneva 1  · Alexei V. Chernyshev 2,3  · Irina A. Ekimova 1,3  · Neonila E. Polyakova 2  · Dimitry M. Schepetov 1,4  · Sergei V. Turanov 2  · Tatiana V. Neretina 1  · Elena M. Chaban 5  · Vladimir V. Malakhov 1,3 Received: 13 July 2018 / Revised: 16 November 2018 / Accepted: 19 November 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract 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, clarifed its species composition in the White Sea, and identifed 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 difered among the three species, which may have resulted from diferent 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. Keywords Lineus · Nemertea · Integrative taxonomy · Field identifcation · Arctic · Population genetics Introduction Lineus ruber (Müller 1774) and L. viridis (Müller 1774) are the most abundant nemertean species that inhabit boreal regions of the Atlantic Ocean and some Arctic seas (White, Barents, Kara and Chukchi Seas; see Chernyshev and Maslakova 2001, 2011). Thus, the “Lineus ruber–vir- idis” species complex is a convenient model for morpho- logical and developmental studies as specimens are easy to acquire for scientists in diferent regions. Previously many zoological studies examined their epidermal ultrastructure (Gontcharoff and Lechenault 1966; Storch and Welsch 1972), proboscis (Gontcharof 1957; Ling 1971), sensory organs (Ling 1970; Storch and Moritz 1971), foregut (Ling and Willmer 1973), nephridia (Bartolomaeus 1985), and other morphological features. Developmental studies of both species (Schmidt 1930, 1941, 1964; Gontcharof 1960; Alluchon-Gerard and Gontcharof 1970) are often cited in many textbooks (Schmidt 1953; Gontcharof 1961; Ivanova- Kazas 1975; Friedrich 1979). Several detailed investigations also examined their regeneration capabilities (Gontcharof 1951; Bierne 1962; Zhuravleva et al. 1970). Lineus ruber and L. viridis were described by O.F. Müller (1774) more than 200 years ago. However, the original description did not provide sufcient information on the morphology and sampling locations of these species (Gibson 1995). Subse- quently, many zoologists referred to these nemerteans as a Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00300-018-2438-7) contains supplementary material, which is available to authorized users. * Alexei V. Chernyshev nemertea1969@gmail.com 1 Lomonosov Moscow State University, Leninskie gory 1/12, Moscow, Russia 119234 2 National Scientifc Center of Marine Biology, Far Eastern Branch RAS, Vladivostok, Russia 690041 3 Far Eastern Federal University, Sukhanova str., 8, Vladivostok, Russia 690950 4 Koltzov Institute of Developmental Biology RAS, Vavilov Str. 26, Moscow, Russia 119334 5 Zoological Institute RAS, Universitetskaya Emb. 1, St. Petersburg, Russia 199 034