Oneirophanta sp.

Oneirophanta sp. MoV. 7333

Material examined. NMV F296845 About NMV *(1) [IN 2021 V04 013] ; NMV F308214 About NMV (1) [IN 2022 V08 117] .

Diagnosis of IOT material. Body elongated, semicylindrical and spindle shaped. Strongly raised dorsally, flattened ventrally, and tapered to rounded oral and anal ends. Smaller specimen ~ 1.5 cm long ( NMV F308214 preserved), larger specimen 16 cm long, 5 cm wide and 3 cm high ( NMV F296845, preserved). Measurements and specific morphology below based on larger specimen. Colour light pink to white with pink or orange tips to tentacles, papillae, and tube feet. Specimens white when preserved. Body wall firm, but not as thick as previous two species. Papillae are long and slender (up to ~ 5 cm long, 0.5 cm wide at base), tapered to a point, and non-retractile. In single to zigzag series on two dorsal radii (~16–18 per side), and single lateral rows (~16 per side). Not crowded mid-body with dorsal body wall clearly visible. Medium-sized tube feet (e.g. 0.8 cm long and 0.4 mm wide) in paired to zigzag series along each ventrolateral radii (~35–36 per side), approximately seven smaller rudimentary midventral tube feet mostly restricted to posterior end. Anus terminal, ventral. Mouth terminal, ventral, ~18 non-retractile tentacles with many small indentations on disc margins (not digit-like and not clearly branching). Body wall ossicles spatulated crosses with smooth arms up to 0.4 mm long and central beam, and rods and crosses with additional irregular branching and perforations, some simple, others joining to form plate-like segments. No complete plates seen. Tube feet with similar though less branching, plus curved simple rods, papillae with distinctive densely packed spatulated rods up to 1.95 mm long.

Remarks. Distinguished from Oneirophanta conservata , O. mutabilis mutabilis and O. mutabilis affinis by spatulated crosses and rods rather than perforated plates as main ossicles. Also distinguished from IOT specimens of O. mutabilis mutabilis by being less robust, more spindle-shaped, white to pink rather than orange, having less crowded dorsal papillae, and lacking digit-like marginal knobs to tentacles. Oneirophanta sp. MoV. 7333 keys to O. setigera ( Ludwig, 1893) using Hansen (1975) based on the presence of spatulated crosses in the body wall, and clusters of spatulated rods in the papillae. However, several differences in the IOT material suggest it is a new species. Both Ludwig (1893) and Hansen (1975) describe and illustrate O. setigera ossicles as only two main kinds: rods with or without perforations, and spatulated crosses with a central beam and long, smooth arms. Rods of the papillae are particularly noted as being long, spatulated, and in bristle-like clusters ( Hansen, 1975). Our specimens have both kinds, but also a third type of more developed rod-plate, in which rods and crosses are developing secondary branching, which in turn is joining to form the beginnings of thick and thin perforated plates. One of our specimens is also much larger (16 cm) than Hansen’s (up to 5.3 cm). Other more minor differences between Oneirophanta sp. MoV. 7333 and those studied by Ludwig (1893) and Hansen (1975) include: tentacle discs with numerous small indentations on the disc margin compared to the eight rounded knobs clearly noted for O. setigera ; additional tube feet: at least five extra per side ventrolaterally and one midventrally; ossicle size for spatulated rods in the papillae, with ours at 1.95 mm for a 16 cm specimen, compared to Hansen’s at 5–6 mm long for a 5 cm specimen. This ossicle size difference is less conclusive however, because ours are closer to Ludwig’s types (specimen size not noted) of O. setigera , which had spatulated rods 1.4–1.7 mm long in the papillae. Oneirophanta sp. MoV. 7333 is also bathymetrically and geographically removed at 1363–1764 m from the Indian Ocean compared to the known O. setigera from the Pacific Ocean: 2104–4064 m Gulf of Panama area, 4540 m Kermadec Trench ( Hansen, 1975), 2912 m Galapagos Islands ( Salinas-de-León et al., 2020), and French Polynesia ( Miller et al., 2017). While likely a new species, the authors are reluctant to identify this IOT material past OTU level Oneirophanta sp. MoV. 7333 without additional investigation of O. setigera comparative specimens and genetic samples.

Distribution. These specimen lots only: Indian Ocean, Australian IOT, Christmas Island Territory, off McPherson Point, 1363–1501 m; Cocos (Keeling) Islands Territory, Rudist Seamount Stn., 1175–1764 m.

References (for genus). Hansen (1975), Ludwig (1893), Miller et al. (2017), Salinas-de-León et al. (2020).