Gilbertaster anacanthus Fisher 1906

Mah, Christopher L., 2023, New Goniasteridae and in situ observations significant to deep-sea coral predation, Memoirs of Museum Victoria 83, pp. 1-35 : 26-28

Gilbertaster anacanthus Fisher 1906

Figures 12 c-d, 13a–g

Gilbertaster ancanthus Fisher, 1906: 1063 ; A.M. Clark, 1993: 223;

H.E.S. Clark & McKnight, 2001: 49; Mah et al., 2010: 272; Atkinson &

Sink, 2018: 417. Gilbertaster brodie McKnight, 1973: 192 ; A.M. Clark, 1993: 223.

Diagnosis. Body stellate, R/r=2.26–3.0, disk thick, arms triangular, interradii weakly curved to straight. Abactinal surface covered by abactinal plates, round to polygonal, each covered by coarse polygonal granules, 1–11 rounded centrally, peripheral granules quadrate, 4–12, surface additionally covered by large bivalve pedicellariae, such that they bisect the plates on which they sit. Marginal plates covered by coarse, smooth polygonal granules identical to those on abactinal and actinal surfaces. Actinal surface adjacent to the adambulacral plates, with prominent bivalve pedicellariae similar in size to the adambulacral plate width. Furrow spines three, subambulacral spines polygonal to angular, 3–6, irregular but uniform in size.

Comments. This represents the first occurrence of this species from the Tasman Sea and Wanganella Bank, the region between Australia and New Zealand. This record is also from significantly deeper (1195–1200 m) than had been previously recorded (277–868 m).

Compared to the holotype of this species from the Hawaiian Islands region , this specimen shows much broader arms and is much less stellate ( R /r=2.26 versus 3.0 in the holotype). Abactinal granules on the holotype are elongate and irregular in shape in contrast to those on this specimen, which are more polygonal to round in shape. Abactinal plates on the arms also occur in many more numerous rows than in the holotype .

Ecological observation. NOAA ship Okeanos Explorer first observed this species in situ in 2017 from the Johnston Atoll region in the North Pacific. The specimen was observed on a vertical, rocky surface in close proximity to the base of a large antipatharian colony. Other hippasterines are known to feed on octocorals and other colonial cnidarians, including antipatharians (e.g., Evoplosoma voratus on Trissopathes in the North Pacific, Mah et al. [2010]). This antipatharian may have been a potential prey item.

Papule of this species, observed on the disk and the proximal regions of the arms, were yellow-brown in colour and fully extended. The remainder of the abactinal surface was a uniform light orange.

Occurrence . Range Extension: Johnston Atoll region, Norfolk Ridge (Tasman Sea), 1200– 1195 m.

Hawaiian Islands, Palau, West New Zealand (east coast). South Africa. 277–868 m.

Images examined. Unnamed Guyot , Johnston Atoll region, 16.72752416° N, 169.3629705° W, 473 m.

EX1706_IMG_20170715T234926Z_ROVHD.jpg

Material examined. NMV F240690 Wanganella Bank, West Norfolk Ridge, Tasman Sea , 34.2389° S, 168.47°E, 1200– 1195 m. Coll. M.F. Gomon & NORFANZ Team , R / V Tangaroa , 3 June 2003. 1 wet spec . R=10.7, r=3.7.