Amphiophiura bakeri, Mcknight, Donald G., 2003

Mcknight, Donald G., 2003, New brittle­stars (Echinodermata: Ophiuroidea) from New Zealand waters, Zootaxa 352, pp. 1-36 : 9-12

Amphiophiura bakeri n.sp. Fig. 3 : A, B, C, D.

Amphiophiura pertusa McKnight, 1993: 175 , 188 (part) (non A. pertusa Koehler, 1930: 227 ).

Material examined: NIWA Stns T243 (1); U568 (19); U569 (1); U571 (2); U572 (1); U584 (2); U585 (6); U590 (6); U608 (1).

Depth Distribution: 865–1769 m.

Geographic Distribution: This species is recorded from north of New Zealand, on the Norfolk Ridge, Three Kings Rise and the Kermadec Ridge.

Description: Holotype NIWA Stn U568: disc diameter 9.5 mm, height 5.7 mm, arms broken, longest at about 18 mm. Disc rounded in outline, evenly domed dorsally, ventral surface flat; disc covered above by a few large tumid plates, the surface finely granulose. At disc centre is a relatively small, pentagonal centrodorsal, with the angles interradial, surrounded by a ring of 5 larger more or less hexagonal radial plates, as wide as long or slightly longer; these abut against the centrodorsal, and their adjacent fellows for about half their length, distally adjacent plates are separated by a large pentagonal interradial plate. The centrodorsal, radials and first interradial have a low central swelling. Radial shields abut against outer end of radial plates; are longer than wide, with angular margins, and united throughout their length. Beyond first interradial plate is a large, hexagonal plate extending to below the rounded margin, adjoining another 4­sided plate that meets oral shield. Interradial plates at margin and on ventral surface almost smooth. Genital clefts extending from the oral shields up side of arm base, genital scale widest dorsally, radial margin with a continuous series of short, flattened, blunt­tipped papillae, these becoming slender blunt spinelets of the arm comb. Arm comb just extends onto dorsal arm surface. Oral shield large, longer than wide, bluntly pointed proximally, widening in distal half, distal margin straight. Adoral shields crescentic, margins parallel; they meet within, extend distally to first lateral armplate. Oral plates with 8–9 small, pointed oral papillae, and 4–5 slightly larger apical papillae at tip. Teeth flattened, blunt, in a single vertical series. Second oral tentacle­pore opens almost on first ventral armplate, with a narrow depression extending to oral slit, with 2–4 flattened papillae along each margin, distal papillae are usually longest.

Arms higher than wide at base, subtriangular in cross­section, dorsal side slightly flattened. First 9–10 dorsal armplates in contact, then slightly separated; plates are small, first is rectangular, wider than long, from about fifth longer than wide, becoming narrowed proximally, so that from about the tenth they are subtriangular. Lateral armplates extending up sides of arms, meeting narrowly at about the tenth, increasingly so beyond, on ventral surface meeting from about the third. Plates have 2 small, peg­like armspines placed at ventrolateral margin of arm, either spine the longest, maximum length 1/2 arm segment; lower spine is adjacent to tentacle­scales. Ventral armplates separated from about the third, plates are wider than long, from third with a blunt proximal point. Ventral armplates and ventral surface of lateral armplates with low transverse sculpture, wrinkling the surface. Tentacle­pores conspicuous over all of remaining arm, basal pores with 4–5 short, flattened scales on proximal margin, outer adjacent to the lower armspine; distal margin with 2–3 flat papillae; distally there are usually 2, sometimes 3 smaller proximal scales, and one distal, the latter becoming a very small spine near end of arm, often missing.

Colour (Preserved specimens) dull cream or uniform light brown, ventral surface sometimes a little lighter.

Etymology: Named for Dr A.N. Baker, a valued friend and colleague.

Holotype: Deposited in the NIWA collection, Wellington No. H­820 (Stn U568).

Paratypes: Deposited in the NIWA collection, Wellington No. P­1372 (Stn U568, 18 specimens).

Remarks: This species is closely related to A. pertusa Koehler , sometimes occurring with it. Some 55 specimens of A. pertusa and 39 of O. bakeri have been examined, and the differences noted appear to be constant. A. pertusa has swollen, coarsely granulate dorsal disc plates, with depressions between them, and the angles of the centrodorsal are radially aligned while A. bakeri n.sp. has relatively smooth dorsal disc plates, lacking any depression between them, and the angles of the centrodorsal are interradial. It is also related to A. turgida Koehler , A. fisheri A.H. Clark , and possibly others. All four have a high, domed disc and no secondary disc plates so that the primary radials touch both centrodorsal and the radial shields; this group may warrant separation as a separate genus or subgenus. Arm structure in all 4 species is very similar.

I have examined specimens of all 4 species and would separate them thus

1: A single large plate between oral shield and that at dorsal margin; 2 plates from oral shield to primary interradial; radial shields usually longer than wide .......................... 2

1: Two or more plates between oral shield and that at dorsal margin; 3–4 plates from oral shield to primary interradial; radial shields usually wider than long ........................... 3

2: Disc plates swollen, coarsely granulose, separated by grooves, with round depressions between and mostly rounded in outline; centrodorsal pentagonal to stellate, angles radial ....................................................................................... Amphiophiura pertusa Koehler

2: Disc plates slightly swollen so that profile is relatively smooth; plates with fine granulation and slightly depressed margins, lacking any rounded depressions between them, with angular outlines; centrodorsal pentagonal, angles interradial ................................ .............................................................................................. Amphiophiura bakeri n.sp.

3: Two elongate plates, side by side, distal to the oral shield, which has a straight distal margin ........................................................................... Amphiophiura turgida Koehler

3: Two triangular plates distal to the oral shield, which has a median distal point separating them ..................................................................... Amphiophiura fisheri A.H. Clark

Figures

FIGURE 3: Amphiophiura bakeri n. sp. holotype, disc diameter 9.5 mm. A: dorsal, B: ventral; paratype, C: dorsal (SEM), D: ventral (SEM). Ophiura (Ophiuroglypha) verrucosa n. sp. holotype, disc diameter 17 mm, E: dorsal, F: ventral.