The heteronemertean genus Lineus Sowerby, 1806 has been badly in need of revision because of its apparent nonmonophyly.
In this paper, we focus on Lineus torquatus Coe, 1901, one of the heteronemertean species that occur
commonly in waters around the North Pacific, as well as a few other allied species distributed in the western North Pacific,
including Lineus alborostratus Takakura, 1898 and Cerebratulus montgomeryi Coe, 1901. Based on phylogenetic analyses
using 16S, COI, 28S, 18S, and H3 gene and ITS sequences, we detected a well-supported clade comprised of
heteronemerteans with a frontal white band on the head, to which we add Kulikovia gen. nov. This genus is nested within a
more comprehensive, highly supported clade, here named the Siphonenteron-clade, which contains Tenuilineus bicolour
(Verrill, 1892), Lineus flavescens Coe, 1905, Siphonenteron bilineatum (Renier, 1804), S. cf. bilineatum, Lineus cf.
caputornatus, and Lineus sp. from Guam. Our analyses confirmed the presence of a cryptic species of what was formerly
known as the cherry-red and reddish forms of Lineus torquatus, herein described as Kulikovia manchenkoi sp. nov. based
on some external characters, internal morphology, and the four genetic markers (COI, 16S, H3, and ITS). In contrast to the
species pair K. torquata–K. manchenkoi, the reddish form of K. alborostrata does not differ genetically from the typical
form of this species. The significance of the external and internal characters for distinguishing cryptic species is discussed.