Benthodytes Théel, 1882

Genus: Benthodytes Théel, 1882 View in CoL

Diagnosis (following Hansen, 1975). Anus dorsal. Unpaired dorsal appendage absent. Circumoral (or post-oral) papillae present. Tentacles soft, pliable and retractile.

Remarks. Benthodytes species are typically elongate, purple to violet-red in colour and have a brim but no unpaired dorsal appendage. Some species have been observed to swim using s-shaped undulations when required ( Miller and Pawson, 1990). The genus is found worldwide at depths of 768–7250 m. Of the ten species currently accepted, four have been previously recorded from Australia: B. lingua , B. sanguinolenta , B. sibogae and B. typica (AFD and WoRMs, 2024). Fourteen lots of Benthodytes were recorded from the IOT at depths of 1304– 4990 m, with nine lots further identified to OTU species level as follows: Benthodytes cf incerta (7 lots), Benthodytes cf sanguinolenta (1 lot), Benthodytes sp. MoV. 7319 (3 lots), and Benthodytes sp. MoV. 7388 (2 lots). Benthodytes is paraphyletic based on COI, and there is insufficient 16S data to infer the true topology. For COI, within the clade containing Benthodytes , the IOT sequences form four well-supported clades: 1) Benthodytes cf incerta , which is sister to B. manusensis ; 2) Benthodytes sp. MoV.7319 which is basal to clade 1, B. manusensis , B. palauta , and B. marianensis ; 3) Benthodytes cf. sanguinolenta , which groups with B. sanguinolenta from the southern Pacific Ocean and B. cf sanguinolenta from the CCZ in the eastern Pacific Ocean; 4) Benthodytes sp. MoV. 7338. The first two clades group together and are sister to Psychropotes . The last two clades are sister to each other and form a distinct lineage from clades 1, 2 and Psychropotes (fig. S1).