Bathyplotes Östergren, 1896

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 : 277

Genus Bathyplotes Östergren, 1896

Diagnosis. (following SolÍs-MarÍn, 2003). “ Synallactidae with 15–20 tentacles; mouth ventral, anus dorsal, subdorsal or nearly terminal. Skin rather thick. Body with sole-like ventral side, usually with marginal appendages; midventral ambulacrum naked or provided with a few tube feet; ventrolateral ambulacral with tube feet in a single row or more. Dorsally, papillae more or less distinctly in rows. Tube feet well developed ventrolaterally but are often lacking midventrally. Dorsal side with double row of papillae along each radius. Musculature in most cases undivided; genital organs in two tufts, located on both sides of mesentery. Calcareous ring weakly developed, sometimes completely absent. Ossicles: Tables with cross shaped disc and a spire built up of 4 rods, usually with several cross beams; “C” shaped bodies maybe present. Ossicles in tentacles, simple or branched rods, sometimes smooth, sometimes spiny.”

Remarks. Cosmopolitan genus with 25 species accepted worldwide, five of which are currently known for Australia: Bathyplotes monoculus , B. moseleyi , B. natans , B punctatus , and B. sulcatus (ALA and WoRMS 2024) . Bathyplotes is closely related to Synallactes and can be difficult to distinguish based on external morphology. Distinguished by Bathyplotes having predominantly four-pillared tables ossicles, compared to the single-pillared ones seen in Synallactes . The Bathyplotes sequences included in the COI and 16S phylogenetic analyses indicate that the genus is paraphyletic and IOT samples exclusively comprise four of the main lineages within the clade (fig. S5). Interestingly, Synallactes cf. crucifera is highly supported as the sister lineage to the B. moseleyi and B. bongraini group, suggesting an in-depth revision of both genera and likely the family is needed. Specimens here showed similarities to B. moseleyi , B. natans , and B. sulcatus . We have identified tissuesampled specimens to sp. MoV. OTU level and kept others at genus level due to crossover between characters in our specimens and issues with clearly defined morphological and ossicle characters for the species within the genus. Twenty lots of Bathyplotes were recorded from the IOT voyages at depths of 1110–1991 m, with 13 lots further identified to OTU species level as follows: Bathyplotes sp. MoV. 7340 (4 lots), Bathyplotes sp. MoV. 7341 (6 lots), Bathyplotes sp. MoV. 7342 (3 lots). One further lot with both Bathyplotes and Synallactes -like characters is identified as Synallactidae sp. MoV. 7339 (1 lot).