Dictenophiura platyacantha, Mcknight, Donald G., 2003

Mcknight, Donald G., 2003, New brittle­stars (Echinodermata: Ophiuroidea) from New Zealand waters, Zootaxa 352, pp. 1-36 : 20-22

Dictenophiura platyacantha n.sp. Fig. 6 : C, D, F.

Amphiophiura urbana McKnight 1989: 3 (non Ophioglypha urbana Koehler, 1904 ).

Material examined: NIWA Stns I730 (15); I740 (7); I741 (3); I743 (30; I744 (6).

Depth Distribution: 288– 328 m.

Geographic Distribution: This species is recorded from Capel, Nova and Argo Banks in the northern Tasman Sea.

Description: Holotype specimen: disc diameter 14 mm, longest arm broken at 32 mm (I744). Disc flat above and below, margin vertical; dorsal surface of disc with numerous plates, varying in size and shape, most slightly tumid. The centrodorsal is pentagonal with blunt radially directed angles, and touching these are 5 larger, 4­sided radial plates; 2 smaller angular plates flank their distal margins, followed by a wedge of 2 plates, the inner larger, these separating radial shields for over 1/2 their length. Radial shields slightly tumid, but lower than other disc plates. Radial shields extend inwards for nearly 1/2 disc radius, and slightly overlap near distal end; at distal end they are separated by inner end of first dorsal armplate. The shields are broad and rounded at outer end, tapering inwards to a point; the 2 shields of a pair differ slightly in shape and size. In the interradii a small roughly 4­sided plate abuts the sides of the centrodorsal, followed by a larger plate, also 4­ sided, which extends to just past the inner ends of radial shields; 2 small plates follow, then one larger at the disc edge. Across the margin, between the genital scales (plates), are 3 plates, outer 2 triangular with base uppermost, and a larger central near rectangular plate. A few much smaller plates may also be present at, or near margin. The ventral surface of disc has up to 6 small scales at and around distal end of oral shield. Oral shields large, covering most of the ventral surface, longer than wide; proximal third tapers to an inner point, outer part equal in width throughout, distal margin very slightly convex. Adoral shields meet within, where they taper to a point, slightly narrowed distally where they extend almost to the widened part of the oral shield. A single pointed apical papilla at tip of jaw, flanked by 1, sometimes 2 similar oral papillae; there are 2–4 distal oral papillae, each low with a small sharp point, contiguous and sometimes confluent. Second oral tentacle­pore opens near end of oral slit, but not into it; both margins of pore have up to 7 small scales, largest distally. Those on the outer margin are on the oral plate and first ventral armplate; those on the inner margin are on the adoral shield. Genital scale narrow on ventral surface, with a small narrow plate alongside the distal part of the oral shield, followed by an elongate plate, widening dorsally and extending across part of distal edge of radial shield.

Genital slit extends from near proximal end of oral shield to margin. Genital scale with minute papillae ventrally, becoming larger at the margin and in the armcomb; on the sides of arms and outer part of the armcomb they are often flattened, sometimes widened near the tip; a few inner spinelets of the main armcomb are round and blunt.

Arms wider than high, broadly rounded basally, gradually tapering and becoming more cylindrical. Dorsal armplates in contact to near end of incomplete arms. First dorsal armplate small, separating outer ends of radial shields, triangular, on some arms of individual specimens may have a transverse division; second plate much wider than long, tapering to a lateral point. Secondary arm comb of very small, fine spines extends from lateral point of this plate onto outer part of first; it is almost entirely hidden by that on the genital scale. Third plate is just wider than long, the rest gradually becoming longer than wide; first few plates are 6­sided, widest just beyond mid­length; dorsal margin narrows as the length increases, so that distal plates are teardrop­shaped. Lateral armplates quite conspicuous from above, and project near the rounded ventrolateral angle. First lateral armplate very long and narrow, with 2 short spines near outer end, close to outer end of oral shield; both spines are short and stubby, outer may be flattened and leaf­like. Second plate with 2 or 3 spines, the lower by the tentacle­scales is stubby, round and pointed, 1–2 or all are flat and pointed, arising from a thin cylindrical base. Third to sixth plate with 3 spines, the lowest round and blunt at the tip, the next flat and pointed, the upper round and sharply pointed. This flat median spine is the longest, almost equal to one arm segment. The more distal plates have 3 spines that become closer together, the median the longest and thickest, length equal to 1/3 arm segment. Ventral armplates in contact for first 6–8 plates, then slightly separated, more so distally, but never far apart, all wider than long. First ventral arm plate wider than long, 6­sided, widest just beyond mid­length, distal margin short and straight: second plate larger, 4­sided; proximal and distal margins straight, the latter widest, lateral margins concave in distal half around tentacle­pore. Succeeding plates become narrower proximally, so that sixth is pointed proximally, widest distally, the lateral margins short. Tentacle­pores conspicuous proximally, but decrease in size, and from about mid­length are small and placed at edges of arm. Basal pores with 3 outer scales, and 2 inner; outer flat and rounded, inner low and long, on lateral plate; sometimes one small scale on ventral plate. At fifth pore there is a single long inner scale extending from ventral to lateral plate and by the seventh there are none. Outer scales diminish in size and from seventh pore there are 2 small scales, inner then becoming very small and disappearing.

Colour: (Preserved specimens) creamy­white above and below.

Etymology: platyacantha , referring to the flat basal armspines.

Holotype: Deposited in the NIWA collection, Wellington No. H­824 (Stn I744).

Paratypes: Deposited in the NIWA collection, Wellington No. P­1376 (Stn I744).

Remarks: This species is readily distinguished by the flat leaf­like basal armspines, not present in any other species of the genus. The Atlantic species also differ in having a smaller oral shield and more ventral scales or plates, the dorsal armplates are swollen and the ventral armplates are elevated. Of species recorded from the South Pacific Ocean, D. stellata (Studer) has a large marginal disc plate and a large transversely divided oral shield, and the first dorsal armplate may have a longitudinal division; D. ctenophora and D. squamosa with a transversely divided first dorsal armplate have the ventral armplates separated from near the base and they become pointed proximally close to the armbase.

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.