Glaciacantha nizari, O’Hara & Thuy, 2025

O’Hara, Timothy D. & Thuy, Ben, 2025, Seamount ophiuroids from the High Seas of the western Indian Ocean, Zootaxa 5718 (1), pp. 1-88 : 26-28

Glaciacantha nizari sp. nov.

https://zoobank.org/ urn:lsid:zoobank.org:act:

Fig. 8a–m

TYPE LOCALITY. Coral seamount, 41° 21.7673´S, 42° 54.9067´E to 41° 22.4´S, 42° 54.6´E, 740 m

TYPE MATERIAL. — JC066 : stn 4-37, Coral seamount, 41° 21.7673´S, 42° 54.9067´E to 41° 22.4´S, 42° 54.6´E, 740 m, 20/11/2011, holotype: 1 ( NHMUK 2025.62 ); paratype: 1 ( NHMUK 2025.61 ); paratype: 1 ( MV F321040 ) ( DNA code=02VSH) .

COMPARATIVE MATERIAL EXAMINED. Glaciacantha cryptum ( McKnight, 2003a) : SS02/2007/37, Mini Matt SSW, 44° 14.654´S, 146° 9.899´E to 44° 14.95´S, 146° 9.656´E, 1120–1380 m, 5/4/2007, MV F144887 ( DNA code=F144887). Glaciacantha doederleini (Hertz, 1927) : PS77/235-3, 65° 32.83´S, 61° 37.29´W, 300 m, 2/3/2011 , BAS ( DNA code= BAS007 ) . SOMUB/73 -BT-4, King Haakon VII Sea, 65° 12´S, 2° 38.76´E, 1210 m, 29/3/2019 , ZMBN 138680 ( DNA code= ZMBN 138680 ). Glaciacantha dubium ( Koehler, 1901) : CEAMARC/48EV194, Eastern Antarctica, 66° 56.366´S, 144° 41.148´E to 66° 56.322´S, 144° 37.245´E, 325–409 m, 29/12/2007, MNHN IE.2009.6515 ( DNA code=2009.6515). Ophiocten banzarei Madsen, 1967 : BANZARE/41, off Enderby Land , 65° 48´S, 53° 16´E, 193 m, 7 paratypes , SAM K1303 . BANZARE/42, off Enderby Land , 65° 50´S, 54° 23´E, 220 m, 3 paratypes , SAM K1304 .

Diagnosis. Disc with thickened rounded scales and triangular radial shields (1/6x dd), lacking disc granules or spines, and lacking arm comb papillae and genital granules. Oral shields 2x as wide as long. Arms with contiguous DAPs, separate VAPs with convex distal margins and a small point proximally, and 4 slender pointed arm spines to 1.5x as long as a segment, with the ventralmost one becoming hook-like distally.

Description. Holotype 6 mm dd, disc pentagonal, covered in round disc plates of various sizes, centrodorsal round and prominent, primary plates not as notable, 6 scales between centrodorsal and interradial margin, scales with fine perforations, covered in a thin epithelium with tiny ossicles in the centre of the disc; radial shields 1/6 dd, rounded triangular, a little longer than wide, divergent proximally, just separated distally, 5 marginal interradial scales between radial shields, centre one a little larger than the others; disc higher than arms but without comb. Ventral disc surface covered by 4–5 transverse rows of small scales, no genital papillae. Oral shield 2x as wide as long, pentagonal, with an obtuse angle proximally, straight distal edge and short lateral edges; adoral shields bar-like, 4x as long as wide, slightly separated interradially; visible portion of the oral plates thicker than adoral shields, meeting proximally separated distally by the 1st VAP. Spiniform teeth, 3x as long as wide, ventral tooth and infradental oral papillae pointed but smaller, 2x as long as wide, inner lateral oral papillae squarish and close together, distal one 2x as wide as long; 2nd oral tentacle pore opening outside of slit, small with 3 adradial and 3 abradial rounded scales that do not fully close the pore.

Arms 4.5x dd; DAPs rhomboidal, as wide as long, widest distally, with distal margin slightly convex, contiguous, becoming long triangular plates distally, 2.5x as long as wide, just contiguous, but separate near the arm tip; LAPs with a raised flange that bears the arm spines; 1st VAP elliptical to fan-shaped, wider than long, with a convex distal margin and straight lateroproximal sides meeting in a small furrow near the end of the jaw slit; 2nd VAP just wider than long, roughly oval, with a convex distal margin and tapered lateroproximal sides; succeeding plates almost semicircular but produced into a small point proximally, by the middle of the arm the plates are broadly oblong, 2x as wide as long, all VAPs separate, but the separation distance becoming progressively greater down the arm; arm spines slender with a sharp tip, 2 on first segment, 3 on 2nd, to 5 on next segments, upper spine longest to 1.5x segment in length, lower ones almost a segment in length; 4 then 3 spines distally, to 3/4 a segment in length, lower spine becomes hook like with a curved tip and ventrally directed thorns by the middle of the arm; tentacle pores small, one oval scale on the lateral arm plate, 1/4 the length of the VAP, opposed by 1–2 rim-like scales around the basal pores, becoming longer and more slender in the middle of the arm, 2x as long as wide and 1/2 the length of the associated VAP. Colour (preserved) dirty white.

Paratype variations. MV F321040 is a similar size and shape to the holotype, with more concave interradial disc margins; to 6 teeth in an irregular vertical series. NHMUK 2025.61 is 5 mm dd. Internal ossicles obtained from paratype MV F321040 . LAPs ( Fig. 8j–k ) quadrangular in lateral view, higher than long, with a bent ventral section that meets the opposing plate on the ventral midline; stereom dense except around the arm spine articulations. Arm spine articulations spaced regularly in a row near the distal LAP border, upper 3 have a raised rim in an asymmetrically circular or spiral shape that do not meet dorsally; lower 2 articulations are sunken into the stereom; distal LAPs ( Fig. 8l ) 2x longer than high. Vertebrae ( Fig. 8h ) zygospondylous with a small zygosphene and wing like zygocondyles .

Distribution. Coral seamount ( 740 m).

Remarks. O’Hara et al. (2018) resurrected the genus Glaciacantha Fell, 1961 for two Ophiocten -like species G. dubium ( Koehler, 1901) and G. doederleini (Hertz, 1927) that occur in the Ophioprygidae, having hook-like lower distal arm spines, thickened disc plates, disc granules or spines, and lacking an arm comb and genital papillae. In addition, our DNA data indicates Ophiocten cryptum McKnight, 2003a is also a member of this clade. Although it lacks disc granules or spines, it does have thickened disc plates, hook-like distal lower arm spines, and no arm comb or genital papillae. Ophiocten banzarei Madsen, 1967 is also very similar, with a similar disc and arms to G. cryptum and no arm comb or genital papillae, although we could not confirm the presence of hooked distal arm spines on the broken paratypes we have examined. Nevertheless, we consider both O. cryptum and O. banzarei are better placed in Glaciacantha . DNA evidence also supports the inclusion of O. cryptum within Glaciacantha ( Fig. 2a ).

The new species is most similar to G. cryptum in lacking disc granules and spines. It differs mainly in the shape of the oral shield, which is almost as long as wide, with a produced acute angle proximally. Glaciacantha dubium has a series of small spines that surround the larger disc plates, and up to 10 arm spines. Glaciacantha doederleini has larger conical spines on irregular bases that cover the disc.

Etymology. Named after Nishath Mohamed Nizar who photographed many of the specimens for this paper.

Figures

FIGURE 2. Maximum likelihood phylogeny of the ophiuroid samples from JC066 and MD208 expeditions and comparative specimens. The phylogeny was created from 275 kb of nuclear DNA and 1431 bp of mitochondrial COI using RAxML v.8.1.20 47 GTRCAT model with 4 partitions (3 exon codon positions and COI) and converted to a chronogram using TreePLv1.0 and 11 fossil-based calibration points. Green samples are from Walters Shoal, blue samples from Coral, purple from Melville, and red samples from Atlantis Bank. Node labels are RAxML fast-bootstrap values (n=100). The tip labels are composed of the species name, sample code, bp of nuclear (415 genes) and mitochondrial (COI) DNA, geographic and depth distribution. Geographic codes:AN=Antarctic, AR=Arctic, AU=S Australia, EA=E Atlantic, EP=E Pacific, IN=Indian, IP=Indo-Pacific, NA=N Atlantic, NEP=NE Pacific, NWP=NW Pacific, NZ=New Zealand, SA=S Africa, SK=Kerguelen, SM=S America, WA=W Atlantic; depth codes: S=Shelf, B=Bathyal, A=Abyssal. (a) the orders Euryalida and Ophiurida, (b) Ophiacanthida and Ophioscolecida, (c) Amphilepidida and Ophioleucida.

FIGURE 8. Glaciacantha nizari sp. nov. holotype NHMUK 2025.62 (a) dorsal view, (b) ventral view, (g) lateral arm base; paratype MV F321040 (c) ventral view, (d) dorsal view, (e) whole animal, (f) distal arm segments showing hooked dorsal arm spines; paratype MV F321040 (h) vertebra distal view, (i) arm spine (broken at tip), (j) proximal lateral arm plate exterior view, (k) proximal lateral arm plate interior view, (l) distal lateral arm plate exterior view, (m) ventral arm plate.