Ophiacantha exilis (Koehler, 1922)

Fig 16d–g

Ophiomitrella exilis Koehler, 1922a: 110–111, pl. 22(9,10).

Ophiacantha exilis . — O’Hara & Stöhr, 2006: 49, 89. — O’Hara, 2024b: 39, fig. 39.

STUDY MATERIAL. — MD208: stn CP4915, Walters shoal, Plaine Sud, 33° 56.85´S, 44° 0.07´E to 33° 58.8´S, 43° 55.3999´E, 1865–2058 m, 12/5/2017: 1 (MNHN IE.2016.1370) (DNA code= IE.2016.1370) .

COMPARATIVE MATERIAL EXAMINED. Ophiacantha exilis (Koehler, 1922a): IN2015_E02/021, Huon Commonwealth Marine Reserve, 44° 19.35´S, 147° 19´E to 44° 19.17´S, 147° 18.47´E, 2028 m, 11/4/2015, MV F227369 (DNA code=F227369). IN2017 _ V03 /069, Hunter CMR, 32° 28.74´S, 152° 59.64´E to 32° 30.42´S, 152° 59.46´E, 1006–1036 m, 3/6/2017, MV F239929 (DNA code=F239929). IN2021 _ V04 /40, Shcherbakov Seamount, 10° 55.475´S, 104° 36.687´E to 10° 55.441´S, 104° 38.0688´E, 1608–1663 m, 14/7/2021, identified by O’Hara (2024b), MV F305548 (DNA code=F305548). TN228/RD2, A1 Seamount, Huon, 44° 19.667´S, 147° 16.48458´E, 1253–1273 m, 20/12/2008, MV F168108. Ophiacantha richeri O’Hara & Stöhr, 2006: TAN1402/31, Forde Seamount, Stratum 1, 35° 19.01´S, 170° 27.09´W to 35° 18.48´S, 170° 27.53´W, 1205–1600 m, 11/2/2014, NIWA 95821 (DNA code=NIWA95821).

Distribution. E Indo-W Pacific (1280–1663 m), S Australia (1006–2518 m), Walters Shoal (1865–2058 m).

Remarks. The single MD 208 specimen measures 2 mm dd. It has the characters of O. exilis including a petaloid disc that is indented interradially; moniliform arms that curl under the disc; small slender disc spinelets, pedicel with 3–5 terminal thorns, sometimes smaller thorns on major ones; thorny arm spines that are short except the uppermost one near the arm base; one tentacle scale that is acute and thorny, to half the VAP in length; 3 oral papillae, the outer one pointed; and adoral shields that extend around the lateral tip of the oral shields. It differs a little from the type and specimens reported by O’Hara (2024b) in having lozenge-shaped oral shields that are only a little extended proximally. On specimens from Australia, the oral shields have a long pointed proximal extension that can separate the adoral shields, and the oral papillae are more spiniform. DNA evidence indicates that this species ranges across the Indian Ocean to SE Australia.