A histology-free description of the branched-proboscis ribbonworm Gorgonorhynchus albocinctus sp. nov. (Nemertea: Heteronemertea)

Abstract

A new species of heteronemertean with branched proboscis, Gorgonorhynchus albocinctus sp. nov., is described based on the external feature and DNA sequences from a specimen collected subtidally among coral rubbles at a depth of about 6 m in a reef area around Taketomi Island in the Yaeyama Islands, southwestern Japan. It can be classified in the genus because the mode of proboscis branching is dichotomous, rather than alternating laterally. From the two known congeners G. repens Dakin and Fordham, 1931 and G. bermudensis Wheeler, 1940, the new species can be differentiated by having a brown body colour with a white band near the tip of the head. The new species is placed in a molecular phylogenetic context with a maximum-likelihood analysis using the nuclear 18S rRNA and 28S RNA genes, as well as the mitochondrial cytochrome c oxidase subunit I gene, together with 20 species of heteronemerteans, for which those sequences were available in the public databases. The results indicate that G. albocinctus is closely related to Cerebratulus leucopsis (Coe, 1901), a species that is supposed to have a non-branched proboscis.