Nemertean diversity at the end of the world: histology-free description of three new species and evidence of genetic isolation between Antarctica and South America

Abstract

The exploration of ribbon worm (Nemertea) diversity of the Patagonian Shelf´ (Argentina) has been limited, with only 13species documented or described between 1968 and 2002. Most of these species remain molecularly uncharacterized andhave been observed only once since their initial descriptions. Despite this, a notable proportion of potential novel species hasbeen discovered in the last two decades, though there have been no records of new species since 2002. This study addressesthis gap by providing external morphological features and utilizing the mitochondrial cytochrome oxidase subunit I (COI)gene as a molecular marker for eight species, encompassing four monostiliferous hoplonemerteans, three heteronemerteans,and one palaeonemertean. Among these, three species are entirely new to science: Baseodiscus argentinus sp. nov., Nip-ponnemertes franciscae sp. nov., and Tetranemertes vivianae sp. nov. Furthermore, we confirm the presence and providebiogeographic analysis (haplotype network) and molecular description of two cryptic species, Parborlasia corrugata and P.fueguina, each with distinct distributions—one is confined to Antarctic and Sub-Antarctic waters, and the other is distributedalong the Argentinean Shelf, extending from Buenos Aires to the Marine Protected Area "Namuncurá Burdwood Bank".This work confirmed genetic isolation of the nemertean fauna between Antarctica and South America and the introductionof Cephalothrix hermaphroditica in America from Europe. We also provide biogeography information about the habitatof the same species on the Pacific and Atlantic coasts of South America (C. hermaphroditica and P. fueguina) and the firstrecorded instance of P. fueguina since its initial description.