Synallactidae, Ludwig, 1894

Mackenzie, Melanie, Davey, Niki, Burghardt, Ingo & Haines, Margaret L., 2024, A report of sea cucumbers collected on the first dedicated deep-sea biological survey of Australia’s Indian Ocean Territories around Christmas and Cocos (Keeling) Islands (Echinodermata: Holothuroidea), Memoirs of Museum Victoria (Mem. Mus. Vic.) 83, pp. 207-316 : 289-290

Synallactidae sp. MoV. 7339

Material examined. NMV F296846 * (2) [IN 2021 V 04 013] .

Diagnosis of IOT material. Medium-sized, elongated, almost cylindrical specimens, slightly flattened ventrally (e.g. 14.5 cm long, 3.5 cm wide, 3 high; preserved). Soft, damaged specimens, firm once preserved, with most skin separated from body. Outer skin salmon pink with white warts and bare body light pink to mauve (live). Skin thick and covered dorsally with white warts and some longer radial papillae (not clear rows). All off-white to grey when preserved. Mouth ventral with approximately five tentacles remaining on one specimen, anus terminal. Tube feet (on shed skin) with zigzag double rows of small outer tube feet (presume ventrolateral), single rows of larger tube feet inside that, and four rows of smaller tube feet (two double rows of zigzags) midventral. Body wall ossicles of various types: typical four-armed tables with multiple perforations at the end of arms (arms ~100 μm), though spires not clear; dorsal wall dense with robust four-armed tables ~128 μm in diameter, typically with single perforations at ends of arms starting to branch, a short solid central spire ~72 μm high and topped with a crown of three bifid teeth; very small four-armed tables with completely joined arms forming button-like discs ~33 μm in diameter with four perforations or up to 80 μm with five or more perforations, and spires made of three or more joined pillars ~56 μm high and distally spinous. Rare Cs (~96 μm), and smooth rods (~200 μm). Papillae with four-armed Bathyplotes -style tables with four arms perforated at the ends, distally spinous spire of approximately four pillars with one or two crossbeams towards the top. Robust single-spired tables present in warts/papillae and body wall.

Remarks. Damaged specimens but some features available on skin and body. Distinctly different in size and robustness to Bathyplotes and Synallactes species collected in the IOT, though with some similar external characters to Antarctic species B. moseleyi and B. natans , particularly with dorsal covering of white warts and papillae and ventral tube feet being more numerous. Differs from both in ventral tube foot arrangement and in ossicles with thick single-pillared spire more common than typical Bathyplotes spires with pillars joined by transverse beams. Small tables have closed bases like B. punctatus but are very small with fewer than six perforations and irregular spires. While these ossicles and the combination of ossicles and morphology are not known to fit any current species, due to its damaged nature and without more material to identify further, we identify this lot as OTU Synallactidae sp. MoV. 7339. Presence here of numerous robust single-pillared tables (also seen in other IOT Bathyplotes ) as the dominant ossicle calls into question the single-pillared table vs multi-pillared table division for Synallactes and Bathyplotes . A revision of the group using morphological and genetic evidence is needed.

Distribution. This specimen lot only: Indian Ocean, Australian IOT, Christmas Island Territory, off McPherson Point, 1363– 1501 m.

References. Sars (1868), SolÍs-MarÍn (2003), Sluiter (1901a), Théel (1886a).