Oneirophanta Théel, 1879

Genus Oneirophanta Théel, 1879 View in CoL

Diagnosis. (amended from Hansen, 1975). Tentacles 15–20, unretractile; discs usually with rounded knobs on the margin but never with ramified processes. Circumoral papillae absent. Ossicles spatulated crosses or perforated, one-layered plates; spatulated rods typically present in the papillae.

Remarks. Bioturbation has been studied in this group, which includes at least one “conveyor belt” species ( Oneirophanta mutabilis ) known to eat and excrete continuously ( Moore and Roberts, 1994). It has also been suggested that brood-protection of young occurs in this species ( Hansen, 1975). There are three currently accepted species and two subspecies: Oneirophanta conservata , O. mutabilis (with subspecies O. mutabilis affinis and O. mutabilis mutabilis ), and O. setigera (WoRMS, 2024) . The geographic subspecies division of O. mutabilis has remained since proposed by Hansen (1967), but Rowe et al. (2017) note that the divergence in life history strategies reported by Hansen (1968, 1975) warrant potential treatment at species level. Only O. mutabilis mutabilis (as O. mutabilis ) has been previously reported from off the southern and eastern coasts of Australia (ALA, 2024). Six lots of Oneirophanta were recorded from the IOT voyages at depths of 1175–5414 m, all further identified to OTU species level as follows: O. mutabilis mutabilis (3 lots), Oneirophanta sp. MoV. 7331 (1 lot), and Oneirophanta sp. MoV. 7333 (2 lots). Morphologically, Oneirophanta is distinguished from Deima by unretractable tentacles, absence of circumoral papillae, and a typically elongate (rather than oval) body. Easily mistaken for Orphnurgus glaber , which can also be elongated and orange/ pink with crowded dorsal papillae and large tube feet. As papillae and tube feet arrangement and number are variable across these groups, it is best to separate externally from Orphnurgus by tentacle disc margins (which are ramified/ branching in Orphnurgus but typically knobbed in Oneirophanta adult forms) but more accurate to use the dominant ossicle types, which are transformed rods in Orphnurgus compared to perforated plates or spatulated crosses in Oneirophanta . The genus diagnosis from Hansen above was amended to account for spatulated rods being rare or absent in some specimens, as noted in many of his own observations ( Hansen, 1975). While Oneirophanta is genetically monophyletic, the relationships between the IOT Oneirophanta samples are incongruent between the COI and 16S datasets (fig. S5). In the former, Oneirophanta sp. MoV. 7331 is sister to O. mutabilis mutabilis and Oneirophanta sp. MoV. 7333 is basal to that group. For the latter gene, the relationship between species is unresolved.