Orphnurgus sp.

Orphnurgus sp. MoV. 7318

Material examined. NMV F296870 About NMV * (2) [IN 2021 V 04 037] ; NMV F296872 About NMV * (1) [IN 2021 V 04 040] ; NMV F308243 About NMV (1) and NMV F312854 About NMV (3) [IN 2022 V 08 131] ; NMV F308295 About NMV (1) [IN 2022 V 08 155] .

Diagnosis of IOT material. Body elongated, sub-cylindrical, raised dorsally and flattened ventrally. Small specimens, up to 27 mm long, 6 mm wide and 4 mm high here ( NMV F312854, preserved). Light pink to orange colour, white when preserved. Skin can be semitranslucent exposing the gut, but typically covered in grit, forams, debris etc., and can look messy or shaggy. Body wall can be crowded with ossicles and have a crunchy texture. Papillae typically thin, tapered and in single to zigzag series (~10) along each dorsal radii, and in lateral series above the ventrolateral tube feet (7+).Non-retractile ventrolateral tube feet, ~ 19 in single to zigzag series along each side. Typically bare of tube feet midventrally, but with median line visible. Anus terminal, slightly dorsal. Mouth terminal but turned to ventral, with up to 17 tentacles seen in these specimens. Tentacle discs with lobed and ramified (branching) processes on the margins. Ossicles visible to the naked eye. Dorsally include variable rods, long, short, thick or thin. Some simple, smooth with tapered ends, others long and spatulated or with twisted or flattened ends starting to branch or perforate, others forming crosses with branching or perforated ends. Occasional crosses with ends starting to branch. Ventral ossicles with some of the same but typically with thicker rods, almost dumbbell-shaped with the tips of ends starting to spread, flatten and perforate. Tube feet with longer thick rods with at least one perforation and initial branching at ends. Papillae with similar, but often longer and thinner, plus some curved support rods.

Remarks. Genetically, COI and 16S data shows Orphnurgus sp. MoV. 7318 as a new lineage with high differentiation from its sister lineage O. glaber from the Australian IOT (p-distances: COI = 15.9%, 16S = 6.6%) (fig. S5). The combination of ossicles including long rods with perforated to spatulated ends, very thick rods with flattening, perforating ends, plus crosses, also separates Orphnurgus sp. MoV. 7318 from other IOT material, and from the nine currently accepted species in the genus as described. However, given the confusion over morphological features and ossicle form due to synonymies by Hansen (1975) and subsequent revisions of this group (see Remarks under O. glaber above), the authors are reluctant to take identification past the OTU level of Orphnurgus sp. MoV. 7318 at this stage, with the genus requiring a major review and further phylogenetic and morphological investigation for resolution.

Distribution. These specimen lots only: Indian Ocean, Australian IOT, Christmas Island and Cocos (Keeling) Islands vicinity, 1459–1850 m, including: Apollo Seamount Stn. 1640–1850 m, Shcherbakov Seamount Stn. 1608–1663 m, Cocos (Keeling) Stn. 1589–1896 m, Muirfield Seamount Stn. 1459–1595m.

References (for genus). Fisher (1907), Hansen (1975), Pawson (2002), Thander (1992), Théel (1879), Walsh (1891).