Systematics and phylogeny of the hoplonemertean genus Diplomma (Nemertea) based on molecular and morphological evidence

We provide a redescription of the poorly known distromatonemertean, Diplomma serpentina ( Stimpson, 1855), a species that has not been reported since its original description. One of the freshly obtained topotypes is designated as a neotype. Based on examination of the new material, as well as the type specimens of three known species, we present a taxonomic revision of the so-far monotypic genus Diplomma Stimpson, 1857, which has been regarded as a dubious taxon since 1904. The following three nominal species are transferred to Diplomma: Paramphiporus albimarginatus Kirsteuer, 1965, Poseidonemertes bothwellae Gibson, 1982, and Correanemertes polyophthalma Gibson & Sundberg, 2001. The genus Paramphiporus Kirsteuer, 1965 is regarded as a junior synonym of Diplomma. Comparison of cytochrome c oxidase subunit I gene ( COI) sequences indicates that D. serpentina is distributed in Indonesia, the Philippines, and Japan. Phylogenetic analyses based on partial sequences of nuclear 28S rRNA and 18S rRNA genes, as well as COI, from a selected number of distromatonemerteans fail to specify the sister relation to Diplomma, although it is suggested that the genus is more closely related to Antarctonemertes, Gononemertes, Nemertellina, Tetraneuronemertes, Oerstedia, and Vulcanonemertes, than to Amphiporus, Cyanophthalma, Geonemertes, Malacobdella, Paranemertes, Poseidonemertes, Prostoma, Tetrastemma, and Zygonemertes. (C) 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 695-722.