Ophiocten cryptum Mcknight, 2003, n.sp.

Ophiocten cryptum n.sp. Fig. 5: A, B.

Material examined: NIWA Stns Z10698 (7); Z10703 (1); Z10705 (1); Z10706 (1); Z10727 (2).

Depth Distribution: 870–1013 m.

Geographic Distribution: This species is recorded only from seamounts or hills in the Graveyard area, just north of the Chatham Rise, central New Zealand. It is known from the Diabolical, Ghoul, Scroll and Zombie seamounts.

Description: Holotype, NIWA Stn Z10706: disc diameter 7.5 mm, all arms broken; the longest 28 mm, long, broken near tip. Disc circular in outline, dorsal surface almost flat, slightly depressed towards centre; ventral surface convex, arching upward towards the relatively thin margin. Dorsal surface of disc with a very thin skin in wet specimen, thin imbricating scales and plates clearly visible when dried; primary plates larger and distinct; centrodorsal slightly ovoid, surrounded by a circlet of small scales, mostly widest proximally, and in 2 interradii the scales are enlarged; the primary radials are just outside this circlet and are transversely ovoid; both centrodorsal and the primaries have a minute tubercle, central on the centrodorsal, slightly distal on the radials; beyond the radials are 3 scales in a transverse row, the outer 2 larger and just touching the radial shields; 2 scales followed by 1 more distal separate the radial shields for most of their length. Radial shields longer than wide, slightly curved, extend inwards for almost 1/2 disc radius, in contact at extreme outer edge, where one may overlap the other. No arm comb. In the interradii, scales become larger towards margin; space between the inner ends of radial shields is occupied by one larger plate, rounded distally, at margin is a small plate flanking shields, the intervening space taken by a larger transversely elongate plate. Ventral surface of disc with thin, imbricating scales. Genital clefts extend almost to disc margin; genital scale 2–3 pieces, sutures indistinct; no genital papillae. Oral shield wider than long, acutely pointed proximally, distal margin broadly rounded; adoral shields extend to first lateral armplate, curved and meet within, almost the same width throughout. Oral plates with a pointed apical papilla at tip and 6–7 oral papillae, proximal 3–4 pointed, the rest becoming flat and truncate or with 2 distal points, as though 2 papillae are united. Distal end of oral slit lacks papillae. Second oral tentacle­pore opens outside of oral slit, with 3–4 low, flat papillae on each margin, these rounded distally and almost confluent.

Arms slightly arched above; first dorsal armplate small, subrectangular, second is a truncate triangle, rest are longer than wide, triangular, with a rounded distal margin; at first truncate proximally, pointed from about the fifth; plates in contact to end of broken arm. No papillae on distal margin of dorsal armplates. First lateral armplate does not meet the dorsal plate, the space being skin­covered (this is not a consistent feature on all specimens); proximal plates have 5–6 finely thorny tapering armspines, upper 1–2 equal to 2 arm segments; spine length decreases ventrally, lowest is just less than one segment, has a slightly enlarged base and is almost thorny. From about the sixth plate they project slightly laterally, have 4, then 3 armspines, upper equal to one arm segment, lower sometimes with a slightly hooked tip. Ventral armplates separated from the third; first has a very short, straight proximal margin and is broadly rounded distally; others have an acute proximal point, and a similar rounded distal margin. Tentacle­pores small, first with 3 small, flat, rounded scales on the radial side and 2 on the other; second pore with 2 scales on proximal margin, others with a single pointed scale on proximal margin.

Colour: (Preserved specimens) disc very light brown above and below, arms almost uniform white.

Etymology: cryptum ­ in reference to the known locality, the “Graveyard area”.

Holotype: Deposited in the NIWA collection, Wellington No. H­821 (Stn Z10706).

Paratypes: Deposited in the NIWA collection, Wellington No. P­1373 (Stn Z10698).

Remarks: Paterson et al. (1982) have described species of Ophiocten from the Atlantic Ocean, with notes on the other species, and further comments are given by O’Hara (1990). This new species is quite distinct from O. hastatum Lyman and O. australis Baker, both recorded from the South Pacific Ocean, in having relatively few dorsal disc plates, dorsal armplates much longer than wide, and more armspines; O. centobi (Paterson et al.) has similarly few and large dorsal disc plates, but an arm comb is present, as are genital papillae, and there are 3 armspines. Small skin­covered areas at the arm base are known in O. abyssicolum (Forbes) and in O. bisquamatum Mortensen, both of which have arm combs and 3 armspines; O. banzarei Madsen with elongate dorsal armplates, no arm comb and 4–5 armspines, differs in the shape of the oral shield (as long or longer than wide) and has shorter armspines, while O. dubium Koehler has small spine­bearing plates around the larger disc plates, no armcomb and 4­5 armspines.