A reassessment of the systematics and a proposal for the phylogeny of some cosmopolitan Lineus species (Nemertea)

Abstract

Morphological,behavioural and biochemical characters of 9 cosmopolitan, benthic species of the nemertean genus Lineus are used both to clarify their taxonomy and to discuss their phylogenetic relationships. Data analysis shows that all fissiparous species of Lineus collected in the world seas up to date can be placed in a single species, L. sanguineus, with three recognisable subspecies, L. s. sunguineus, L. s. nigricans and L. s. pseudolacteus. These taxa were originally described as separate species mainly according to their geographic origin under the names L. sanguineus (shores of European seas), L. socialis (Atlantic North American shores), L. vegetus (Pacific North American shores), L. pseudolacteus (shores of the English Channel) and L. nigricans (Mediterranean coasts of Italy and France). Examination of the character value matrix suggests a phylogenetic tree developing from two ancestral branches. The first branch includes the two related species L. ruber and L. viridis, the second branch the three species L. longissimus, L. lacteus and L. sanguineus. This approach to the taxonomic and phylogenetic relationships of Lineus nemertean species is in agreement with the intra-and interspecies histocompatibility data in nemerteans: (i) grafts transplanted from donors to recipients of the same species succeed and grafts transplanted from donors to recipients of different species fail; (ii) grafts are rejected more rapidly when the donor and recipient species diverged earlier in evolution and, a contrario, grafts are accepted better when the donor and recipient species have been more recently isolated.

Population genomics of sexual and asexual lineages in fissiparous ribbon worms (Lineus, Nemertea): hybridization, polyploidy and the Meselson effect

“…Phylogenetic analysis consistently supported the grouping of L. viridis and L. ruber vs. all other Lineus species, in agreement with morphological and immunotransplantation data (Bierne et al 1993). The longissimus group contained species sometimes assigned to genera Ramphogordius (R. sanguineus, R. pseudolacteus) and Riseriellus (Ri.…”

“…Its regenerative abilities are weaker than those of L. sanguineus. Both are related to the sexual L. lacteus and L. longissimus based on morphology, anatomy and immunotransplantations (Bierne et al 1993). This group therefore appears to be an ideal model for the study of genome evolution in asexual vs. sexual contextwith the additional peculiarity that asexual reproduction in Lineus is agametic, in contrast to the other groups of asexuals studied so far.…”

“…For these reasons, they are suspected to reproduce mainly, if not exclusively, in an asexual way in nature, even though reproduction in the wild has never been observed in Lineus. L. sanguineus has a worldwide distribution, and several subspecies have been distinguished based on colour pattern and geographic range (Bierne et al 1993), suggesting a relatively ancient origin of asexuality in this cosmopolitan species. L. pseudolacteus, which so far has only been found in Brittany (France), still lacks any report of an individual with trace of ovary or testis.…”

A phylum-wide survey reveals multiple independent gains of head regeneration ability in Nemertea

“…Pilidiophora (Heteronemertea) is a large and well-supported clade [27,[29][30][31], and many species are frequently cited as examples of nemerteans with outstanding regenerative ability [25,32,33]. However, all of these "many species" [26,28,[34][35][36][37][38][39][40] have now been synonymized to Lineus sanguineus [41][42][43]. Thus, regeneration data remain very cursory across Nemertea but do suggest that high regenerative ability -in particular, the ability to regenerate a head -may be uncommon in the phylum.…”

Yolk proteins during spontaneous and experimentally induced oogenesis in the heteronemertine,Lineus lacteus

“…Most of the information that is available on sexual maturation has been obtained from morphological and histological investigations, with occasional autoradiographic studies (Bierne, 1964(Bierne, , 1966(Bierne, , 1970(Bierne, , 1973(Bierne, , 1983RuC and Bieme, 1978;Bierne and Rub, 1979). While oogenesis and the cytology of the oocyte have been the subject of several studies, relatively little is known concerning the yolk proteins of these animals (Bierne et al, 1993). Biochemical studies have been hindered by the small quantity of available material, the difficulty of obtaining homogeneous classes of oocytes and the *Corresponding author.…”