Abstract
A new species of Osedax is described here using molecular and morphological data. It was found at the depth of 550 m off the Brazilian coast through experimental deployment of cow bones. Osedaxnataliae sp. nov. is the second Osedax species from the Southwest Atlantic Ocean and had been previously reported as Osedax 'BioSuOr-4'. Phylogenetic analysis of five concatenated genetic makers (28S rDNA, Histone H3, 18S rDNA, 16S rDNA, and cytochrome c oxidase I) placed Osedaxnataliae sp. nov. within a well-supported Osedax Clade V, nested within a clade of Pacific Ocean Osedax though with poor support. The minimum interspecific COI distance between O.nataliae sp. nov. and another known Osedax was 13.92% (closest to O. 'sagami-3'). The maximum intraspecific COI diversity (uncorrected) within O.nataliae sp. nov. sampled here was 2.44% and population structure was visualized via haplotype network analysis. Morphologically, O.nataliae sp. nov. is characterized by its reddish orange crown of palps and a ventral yellowish collar on the anterior trunk where it meets the base of the crown. Osedaxnataliae sp. nov. shares features with other Clade V species, notably pinnules inserted on the outer margin of palps. Additionally, the presence of dwarf males within the tube lumen of females was documented. Further sampling and research in the Southern Hemisphere are needed to understand the diversity and biogeography of Osedax across the world's oceans.