Osedax nataliae Gularte, Sumida, Bergamo & Rouse 2024, sp. nov

Osedax nataliae Gularte, Sumida, Bergamo & Rouse sp. nov Figs 3, 4, 5 Osedax ‘ BioSuOr-4 ’ sec. Shimabukuro and Sumida 2019. Type material. Holotype: MZUSP 6201, Female, preserved in ethanol, derived from an experimentally deployed cow bones (Bos taurus) at a depth of 550 m, collected with R / V Alucia on the continental margin off São Paulo state, Brazil (26°36'13.44"S, 46°09'9.29"W) on 18 May 2017. Paratypes: MZUSP 6203 –6204, all females (30), preserved in ethanol, collected on cow bones deployed at the same locality and date as the holotype. Two dwarf male (allotypes), fixed in ethanol from tube of holotype: MZUSP 6202, same date and locality as holotype. Diagnosis and description. Holotype female (Fig. 3 A – C); body length ~ 14.7 mm; gelatinous tube (removed) 0.2 wide, longer than trunk and crown; crown of palps, ~ 2.8 mm long; trunk length ~ 7.4 mm, width ~ 0.5 mm; root structure ~ 4.5 mm long; width ~ 2.4 mm; Crown of four pinnulated palps, with the pinnules arranged along the outer margin of the palps (Figs 3 B, 4). Conspicuous oviduct shorter than palps (Figs 3 B, 4 A – D). Collar ventrally along the margin of anterior trunk, except for the dorsal portion (Figs 3 B, 4 B – E). Live specimens with palps bright red-orange distally, becoming yellow and then white proximally to the boundary with the trunk (Fig. 5). No obvious pigmentation on trunk or demarcation into upper and lower trunk. Root structure missing in holotype, bulbous or lobulate in paratypes. Ovisac an ellipsoidal mass contain oocytes at various stages of development (Fig. 3 A). Dwarf male ~ 170 μm in length, fusiform, no appendage organs (Fig. 3 C); posterior hooks present (Fig. 3 D). Distribution. Known from the continental margin off São Paulo state, Santos basin, Brazil, at a depth of 550 m; on experimentally deployed cow bones. Molecular results. The final lengths of sequences for the different genetic markers were 482–600 bp (COI), 454 bp (16 S), 1769 bp (18 S), 997 bp (28 S) and 309 bp (H 3). Uncorrected intraspecific divergence of O. nataliae sp. nov. for COI was up to 2.44 %. In terms of distance, the most closely related species to O. nataliae sp. nov. was O. ‘ sagami- 3 ’, with a minimum interspecific distance for COI of 13.92 % (Suppl. material 1). The phylogenetic analysis of the concatenated dataset of the five markers placed Osedax nataliae sp. nov. in the well-supported Clade V (see Rouse et al. 2018) although relationships within the clade were poorly supported. The new species was recovered as sister species to the clade formed by O. ‘ sagami- 3 ’, known from NW Pacific at unknown depth, and Osedax roseus, from NW and NE Pacific at depths of 633 to 1820 m (Fig. 6). A total of 22 distinct haplotypes were recovered for the COI dataset (n = 38), with the most common one being shared by ten individuals (Fig. 7). Despite originating from a single experimental lander, the network reveals a central and more common haplotype surrounded by several closely related and some more distant haplotypes with numerous nucleotide substitutions. Remarks. Osedax nataliae sp. nov. is part of the Clade V according to the phylogenetic analysis (Fig. 6) and shares some important morphological features with the other taxa within this clade, such as pinnules inserted on the outer margin of palps (Fig. 4 D, E) and a collar at the base of the crown (Figs 4 B, 5 B – E). The collar of Osedax nataliae sp. nov. and Osedax roseus (the closest species in molecular phylogeny that has a morphological description) are similar in shape and position, though more inflated in O. nataliae sp. nov. Some specimens of Osedax nataliae sp. nov. appear to lack a collar, which could be an artifact of fixation. The dwarf males of O. nataliae sp. nov., with a length of 170 μm, are notably smaller than the males of O. rubiplumus (400 μm – 1.1 mm long) but similar in size to those of O. roseus (130–210 μm) and O. frankpressi (150–250 μm). The body size (length of crown + trunk) of Osedax nataliae sp. nov. females varied markedly among the individuals examined, ranging from 4 mm to 15 mm, with a mean value of 6.76 mm. When compared with groups from the same clade, the body size is like O. roseus, O. bryani, and O. fenrisi females but much smaller than O. rubiplumus. Osedax nataliae sp. nov. is not obviously distinguishable from its relatives on morphology. Its notable features such as the red-orange distal crown of pinnulate palps, yellowing towards the base, collar, and long trunk (Fig. 3) may occur in other species of Clade V, such as O. roseus. However, molecular data from both the phylogenetic analysis (Fig. 6) and COI distance (Suppl. material 1) confirm Osedax nataliae sp. nov. as a new species. Etymology. This species is named after Natalia Gularte, mother of the first author, in recognition of her long and continued support in this research effort.