Ophiacantha otagoensis Fell, 1958

Mills, V. Sadie & O'Hara, Timothy D., 2013, Ophiuroids (Echinodermata; Ophiuroidea) of biogenic habitats on the continental shelf of New Zealand, Zootaxa 3613 (5), pp. 401-444 : 418-420

Ophiacantha otagoensis Fell, 1958 stat. nov.

( Fig. 7 )

Ophiacantha abyssicola otagoensis Fell, 1958: 25 , pl. 4(G, L).

Ophiacantha imago .—McKnight, 1967a: 307 (in part) [Non Ophiacantha imago Lyman T, 1878 ]. Ophiacantha vilis .—McKnight, 1967a: 308 [Non Ophiacantha vilis Mortensen T, 1924 ].

Ophiacantha sollicita .—McKnight, 1984: 144 [Non Ophiacantha sollicita Koehler R, 1922 ]. Ophiacantha brachygnatha .—O'Hara, 1990: 297 (in part) [Non Ophiacantha brachygnatha Clark H L, 1928 ].

Material Examined. Otago. TAN1108/117, NIWA 74740 (4).

Comparative Material. Ophiacantha brachygnatha H.L. Clark, 1928 : TAN0104/336, Zombie Seamount, 42° 46.07´S, 179° 55.31´W, 955– 890 m, 20/4/2001, NIWA 44650 (40). Ophiacantha fidelis (Koehler, 1930) : NZOI/A917, Chatham Rise, 43° 55.98´S, 179° 15´W, 203 m, identified by McKnight (1967a) as Ophiacantha imago , NIWA 79559 (500). S03/84/74, Off Maria Island, 42° 41´S, 148° 25´E, 320–480 m, 25/6/1984, MV F52721 (300). TAN0308/136, South Norfolk Ridge, 33° 23.6´S, 170° 12.38´E to 33° 23.43´S, 170° 11.75´E, 469–490 m, 1/ 6/2003, MV F99716 (500). Ophiacantha otagoensis Fell, 1958 : TAN0803/63, Macquarie Ridge, Seamount 6, 52° 29.24´S, 160° 24.9´E to 52° 29.03´S, 160° 24.55´E, 350–560 m, 9/4/2008, NIWA 40089 (114).

Diagnosis. Disc covered in minute spinelets with 3–6 terminal thorns, radial shields obscured, but visible as raised white bars beneath spines. Dorsal arm plates bell shaped, and separate, though contiguous on basal segments in large animals. Seven arm spines at base, finely thorny, decreasing in length ventrally. Single, narrow and pointed tentacle scale.

Description. See Fell (1958).

Distribution. New Zealand (68–999 m), northern Macquarie Ridge (119–560 m), Tasman Sea (785–820 m).

Remarks. Although Baker & Devaney (1981) synonymised Ophiacantha abyssicola var. otagoensis with O. brachygnatha from south-eastern Australia, we recognise O. otagoensis as a distinct species, differing from O. brachygnatha in having arms that are not particularly moniliform, nor typically curved under their body as in O. brachygnatha . The dorsal arm plates are narrowly contiguous on basal segments of larger animals. There are often notable white bars of colour over the radial shields. Both species have bell-shaped dorsal arm plates, small tentacle scales, and minute disc spinelets with 3–6 terminal thorns. Both species occur in New Zealand, with O. brachygnatha typically epizoic on corals and sponges on seamounts, the arms firmly grasping the host, whereas O. otagoensis appears to occur opportunistically on hard substrata or over sessile organisms. Ophiacantha otagoensis has been found in large numbers on seamounts on the northern Macquarie Ridge ( Fig. 7 ).

Four other south-western Pacific species of Ophiacantha are similar to O. otagoensis . The tropical Ophiacantha pentagona Koehler, 1897 has strongly noded arms with wide dorsal arm plates restricted to the distal edge of the expanded arm "node". Ophiacantha renekoehleri O'Hara & Stöhr, 2006 has elongated adoral plates that extend around the lateral margins of the oral shield. Ophiacantha fidelis Koehler, 1930 has minute sparse disc granules that are microscopically thorny near the disc centre. Ophiacantha fidelis has also been found in dense aggregations off Tasmania (Blaber et al. 1987) and on the South Norfolk Ridge and Chatham Rise (see comparative material examined above). Finally, Ophiacantha vilis Mortensen, 1924 differs in having a much larger tentacle scale, at least 2/3 as long as the ventral arm plate.

Figures

FIGURE 7. Seafloor fields of Ophiacantha otagoensis Fell, 1958 from Seamount 6, Macquarie Ridge (TAN 0803 / 64, DTIS camera).