Astroceras elegans (Bell, 1917)

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 : 407-410

Astroceras elegans (Bell, 1917)

( Figs. 3–4 )

Astroschema elegans Bell, 1917: 7 .

Astroceras elegans .—Mortensen, 1924: 107, pl. 4(3).—Fedotov, 1927: 343.—Mortensen, 1933b: 53–54, figs. 37–38.—Mortensen, 1936: 241.—Fell, 1958: 21.— Baker, 1980: 66–68, figs. 25, 32.—Guille & Wolff, 1984: 7–9, pl. 1(a–b).—Rowe & Gates, 1995: 360.—McKnight, 2000: 42–44, fig. 18, pl. 17.

Astroceras maui McKnight, 1968: 516 –519, figs 4–5 [synonymised by Baker, 1980].

Asteroceras elegans .—McKnight, 1989: 25–26.

Material Examined. Bay of Islands. TAN0906/126, NIWA 55951 (1). TAN0906/132, NIWA 56101 (1). TAN0906/135, NIWA 56201 (1). TAN0906/178, NIWA 77659 (1); NIWA 77660 (3); NIWA 57094 (8); NIWA 57061 (1); NIWA 57090 (1). East Coast North Island. TAN1108/253, NIWA 75614 (2); NIWA 77658 (2). TAN1108/268, NIWA 77650 (1). TAN1108/275, NIWA 77649 (1). Far North. TAN0906/154, NIWA 56500 (1); NIWA 56499 (3). TAN0906/162, NIWA 56735 (2); NIWA 56709 (2); NIWA 56707 (9). TAN0906/164, NIWA 56833 (1). TAN1105/9, NIWA 77648 (4). Three Kings Islands. TAN1105/53, NIWA 73308 (1); NIWA 73308 (1). West Coast North Island. TAN1105/137, NIWA 73831 (1).

Comparative Material. Astroceras elegans (Bell, 1917) : NZOI/C527, Star of bengal bank, 32° 30´S, 179° 12´W, 508 m, 18/9/1960, holotype of Astroceras maui , NIWA 448 (1); paratype of Astroceras maui , NIWA 451 (1); paratype of Astroceras maui , NIWA 449 (1); paratype of Astroceras maui , NIWA 450 (1).

Diagnosis. Disc and arms covered by skin, but ridges of radial shields and structure of arm vertebrae beneath clearly visible. Ventral arm plates do not join in central midline. Five arms (not fissiparous), two arm spines from second arm segment, finely prickly at tip, distally transformed into hooklets. Small uniform granules on radial shields and arms. Though variable, two consistent morphological forms apparent ( Fig. 2 ). One form clearly more tubercular, with numerous irregularly arranged white granules protruding through skin on dorsal disc. Arms do not appear annulated and are solid yellow with dark brown arm spines. Second form with more regularly arranged white granules, not protruding through skin. Arms appear annulated, transversely striped with dark bands of skin.

Description. See McKnight (2000).

Distribution. New Zealand (25–705 m), eastern Australia (143 m), Tasman Sea (308–875 m), New Caledonia (350–705 m).

Remarks. Recently collected Astroceras elegans specimens show remarkable variation in granulation on the dorsal disc and in the banding pattern on their arms. McKnight’s (1968) description of A. maui is closely aligned to the second morphological form described above, while Mortensen (1924) and Baker (1980) describe large variation in granulation/ tuberculation of the disc and arms and A. maui has subsequently been synonymised with A. elegans .

Arm segments from specimens of both morphological forms were treated with domestic bleach to dissolve the skin and allow examination of the granules and arm plates. There are fragmented plates on the lateral side of the arm which show some variation between forms ( Fig. 4 ). Following Mortensen (1933) we interpret these as fragmented lateral arm plates, although to our knowledge their ontology has not been properly investigated. Despite these differences we have not found any consistent morphological characters to differentiate these specimens into two species. Additional genetic and morphological data are required to determine whether A. maui should be resurrected.

Figures

FIGURE 3. Two morphological variations of Astroceras elegans (Bell 1917) (NIWA, TAN 0906 / 154) showing live colour. a: two specimens in situ on host plexaurid coral, scale bar = 1 cm, b: morph 1 cf. A. maui McKnight, 1968 (NIWA 56500), c: morph 2 (NIWA 56499, TAN 0906 / 154).

FIGURE 4. Proximal arm segments from two morphological variations of Astroceras elegans (Bell, 1917) specimens treated with bleach to expose arm plates. a: NIWA 56499, TAN 0906 / 154, morph 2, dd = 10.4 mm; b: NIWA 57061, TAN 0906 / 178, morph 1, cf. A. maui McKnight, 1968, dd = 9.24 mm. Scale bar = 1 mm, g = spiny granule, as = arm spine, lap = laterally placed arm plates.

FIGURE 2. a: Asteroporpa (Asteroporpa) australiensis Clark, 1909 on host primnoid coral (NIWA 56911, TAN 0906 / 170), scale bar = 3 mm, and b: Astrobrachion constrictum (Farquhar, 1900) on host black coral (NIWA 56330, TAN 0906 / 146), scale bar = 10 mm.