A New Heteronemertean Genus with Variable Potential of Anterior Regeneration for Species Formerly Belonging to Lineus (Nemertea: Pilidiophora).

Abstract

The heteronemertean genus Lineus Sowerby, 1805, currently accommodating about 100 species, is known to be non-monophyletic and is in a desperate need of taxonomic revision. In this article, we focus on a group of species including L. caputornatus Takakura, 1898, L. grubei (Hubrecht, 1879) auct., L. pictifrons Coe, 1904, and L. subcingulatus Takakura, 1898. These four morphologically similar species formed a clade to the exclusion of the type species, L. longissimus (Gunnerus, 1770), on a molecular phylogeny based on partial sequences of the 16S rRNA, 18S rRNA, 28S rRNA, cytochrome c oxidase subunit I, and histone H3 genes. For this clade we propose the name Bilucernus gen. nov. We redescribe L. grubei auct. from Japan as Bilucernus takakurai sp. nov. Bilucernus clade was nested within a larger clade that also contained members of Kulikovia Chernyshev, Polyakova, Turanov, and Kajihara, 2017, Lineopselloides Gibson, 1990, Siphonenteron Renier in Meneghini, 1847, and Tenuilineus Riser, 1993. We observed that body fragments from the intestinal region regenerated a head in B. caputornatus comb. nov. and B. subcingulatus comb. nov., but did not in B. takakurai sp. nov. The type specimen of Lineus bipunctatus Takakura, 1898 was most likely a regenerating individual of B. caputornatus comb. nov. We synonymize L. bipunctatus with L. caputornatus, giving nomenclatural priority to the latter. In addition, Lineus albifrons Coe, 1934 is herein also synonymized with L. caputornatus. We speculate that the unusually wide geographic distribution of B. caputornatus comb. nov. is related to its ability to regenerate head from fragments of body.