Rescuing the history of siboglinids in Brazilian deep waters: Neotype designation for the species Siboglinum besnardi Tommasi, 1970 and Siboglinum nonatoi Tommasi, 1970 (Annelida: Siboglinidae)

Two new neotypes designations are proposed for the species Siboglinum besnardi and Siboglinum nonatoi, based on specimens collected from the Southwestern Atlantic deep waters, type locality of both species. This designation is necessary due to the loss of the original type series for both species. Species identities were validated through morphological analyses, and comprehensive redescriptions are conducted for both species, which not only expand upon the original descriptions but also introduce additional diagnostic characters, including stereomicroscope and SEM images. In addition, genetic material from a specimen of Siboglinum besnardi was obtained, enabling a molecular phylogenetic analysis utilizing COI, 16S and 28S molecular markers. This analysis confirmed not only the species placement within the family Siboglinidae but also provided substantial support for the monophyly of the Frenulata, Vestimentifera, Monilifera and Osedax groups within the annelid family Siboglinidae.