Description of a new Osedax (Annelida, Polychaeta, Siboglinidae) species colonizing cow bones in the South Atlantic Ocean

A new species of <i>Osedax</i> 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. <i>Osedaxnataliae</i> <b>sp. nov.</b> is the second <i>Osedax</i> species from the Southwest Atlantic Ocean and had been previously reported as <i>Osedax</i> 'BioSuOr-4'. Phylogenetic analysis of five concatenated genetic makers (28S rDNA, Histone H3, 18S rDNA, 16S rDNA, and cytochrome c oxidase I) placed <i>Osedaxnataliae</i> <b>sp. nov.</b> within a well-supported <i>Osedax</i> Clade V, nested within a clade of Pacific Ocean <i>Osedax</i> though with poor support. The minimum interspecific COI distance between <i>O.nataliae</i> <b>sp. nov.</b> and another known <i>Osedax</i> was 13.92% (closest to <i>O.</i> 'sagami-3'). The maximum intraspecific COI diversity (uncorrected) within <i>O.nataliae</i> <b>sp. nov.</b> sampled here was 2.44% and population structure was visualized via haplotype network analysis. Morphologically, <i>O.nataliae</i> <b>sp. nov.</b> 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. <i>Osedaxnataliae</i> <b>sp. nov.</b> 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 <i>Osedax</i> across the world's oceans.