Ophiura (Ophiura) spinicantha, Mcknight, Donald G., 2003

Mcknight, Donald G., 2003, New brittle­stars (Echinodermata: Ophiuroidea) from New Zealand waters, Zootaxa 352, pp. 1-36 : 23-25

Ophiura (Ophiura) spinicantha n.sp. Fig. 6 : A, B, E.

Material examined: NIWA Stns J658 (numerous); J667 (6); J668 (10); J669 (2); J714 (13); J717 (5); P969 (7); P970 (11); U195 (12); U200 (12); U202 (4); U226 (14); U552 (1); U579 (13).

Depth Distribution: 1585–3480 m.

Geographic Distribution: This species is recorded from deep water in the Bay of Plenty and the Tasman Basin.

Description: Holotype, NIWA Stn U200: disc diameter 16 mm, arms broken, longest at about 26 mm. Disc low, flat above and below, outline pentagonal, interradii slightly rounded. Dorsal surface of disc covered with very numerous small, irregularly­shaped scales, with larger, rounded centrodorsal present, as are similar radial plates, at about 1/2 distance to margin; disc plates become larger towards margin in both radii and interradii. Radial shields almost 2.5 times longer than wide, widest distally, divergent, strongly curved, sharply pointed proximally, extend inwards for about 1/2 disc radius. Radial shields separated proximally by several rows of scales, at distal end by a single larger scale. Ventral surface of disc with numerous small scales. Genital slits long, extending from about middle of oral shield to outer ends of radial shields; genital scales very narrow proximally, but widen near margin on ventral surface; at proximal end, adjacent to oral shield, cleft lacks papillae, beyond on adradial edge are small, low, almost confluent papillae, becoming larger distally, and arm comb comprises short, slightly flattened, blunttipped spines; on abradial side a second dorsal arm comb is developed on side of arm, with much shorter, thinner spines, usually visible but sometimes concealed. Oral shields relatively large, about as wide as long, pointed proximally, slightly constricted at start of genital cleft, widest at the straight distal margin. Adoral shields meet within, extend distally to first lateral armplate, and abutting proximal end of genital cleft. Oral plates with 5 oral papillae along oral slit, not extending beyond second oral tentacle­pore; outer 3 papillae blunt­tipped, subrectangular, inner 2 more pointed; a single, slightly larger pointed apical papilla at jaw apex, sometimes absent; teeth pointed, in a single vertical series. Second oral tentacle­pore conspicuous, opening outside oral slit, proximal or adradial margin with 6–7 flat papillae, more or less aligned with oral papillae, distal or abradial margin with 4–5 similar papillae.

Arms slightly higher than wide at base, gently tapering distally. Dorsal armplates in contact throughout remaining arms; at base, between radial shields are 2–3 small rectangular plates, usually with spinelets of inner arm comb apparent; next 3–4 plates are wider than long, more or less subrectangular; more distal plates are longer than wide, with straight proximal and lateral margins, distal margin slightly rounded and the widest part of plate. Lateral armplates with 2 very slender, delicate armspines, up to about 1/2 length of arm segment; upper spine placed about midway up side of arm, lower close to tentaclepore. First 2 ventral armplates just in contact, remainder separated; first is a broad plate, with a very slight median point on distal margin; second is slightly longer than wide, pointed proximally and subtriangular; the plates then become wider than long with small median points on proximal and distal margins, that on distal margin usually slightly thickened. Tentacle­pores relatively large with numerous tentacle scales; proximal pores with 5–6 scales on proximal margin, outer scale spiniform, slightly spaced from lower armspine, others are small, flat and squarish; distal margin has 4–5 squarish papillae. On distal pores there are 3–4 scales on the proximal margin only, the inner bluntly pointed, the outer spiniform; tentacle­scales are easily dislodged.

Colour: (Preserved specimens) uniform dull grayish­white above, slightly lighter below.

Etymology: spinacantha, referring to the slender delicate armspines.

Holotype: Deposited in the NIWA collection, Wellington No. H­825 (Stn U200).

Paratypes: Deposited in the NIWA collection, Wellington No. P­1377 (Stn U200).

Remarks: Some specimens have a few very scattered dorsal disc spines; that from Stn U552 has oral shields rounded proximally. Specimens from Stns P969 and P970 had ripe gonads.

This species appears to be the first with a double arm comb recorded from the New Zealand region. The double arm comb occurs in several species referred to Ophiura (Ophiura) and also is present in species referred to Dictenophiura .

The most closely related species are O. aequalis , O. ljungmani , O. sarsi , O. leptoctenia and O. bathybia . Both O. aequalis and O. ljungmani have some larger plates or scales on the dorsal surface of the disc, the former also with 4–6 armspines, the latter with a convex distal margin to the dorsal armplates, and 3 armspines, the uppermost longest, equal to an arm segment.

Of the other species, all have 3 armspines; in addition, O. sarsi has short, almost contiguous radial shields, while O. leptoctenia has a slight angle to the distal margin of the dorsal armplates; both species have the oral shield longer than wide. The closest relative appears to be O. bathybia , differing in the distal margin of both dorsal and ventral armplates. One feature of O. spinicantha , not reported for any of the above species, is the supplementary lateral armplate that carries the secondary armcomb; although not mentioned in the other species, it may well have been overlooked. Features of these species are listed below.

Figures

FIGURE 6: Ophiura (Dictenophiura) spinicantha n. sp. holotype, disc diameter 16 mm. A: dorsal, B: ventral, E: armbase. Ophiura (Dictenophiura) platyacantha n. sp. holotype, disc diameter 14 mm., C: dorsal, D: ventral, F: armbase.