Atheraster pheos, Mah, 2023

Mah, Christopher L., 2023, New Goniasteridae and in situ observations significant to deep-sea coral predation, Memoirs of Museum Victoria 83, pp. 1-35 : 6-9

Atheraster pheos n. sp.

urn:lsid:zoobank.org:act:4084989D-EA1D-4137-9D8B-

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Figure 3a–g

Etymology. The species epithet phaeos is Greek for a spiny plant alluding to the prickly spines present on the marginal plates.

Diagnosis. Body strongly stellate (R/r=3.4), arms elongate, arm tips strongly upturned. Abactinal plates bare with no accessories. Abactinal arm plates larger than those of disk, but gradually changing proximally on each arm. Marginal plates bearing 6–10 spines, interradially with a single prominent conical spine on arm spines. Pedicellariae paddle-shaped. Nearly all actinal plates with a prominent paddle-shaped pedicellaria, pointed granules. No actinal spines. Furrow spines, 6–9, spines blunt, quadrate. Proximal adambulacral plates, adjacent to furrow spines, large paddle-shaped pedicellariae, valves rectangular and edges smooth, succeeded distally by subambulacral spines, four to each plate.

Comments. Rather than a single large conical spine, most proximal marginal plates on A. pheos variably display 3–4 short spines, with a single spine on more distal plates.

This species very closely resembles A. arandae , with which it shares the presence of multiple spines on the interradial marginal plates in conjunction with more pronounced single spines on the distal marginal plates. It differs in possessing fewer furrow spines (6–9 versus 12–15 on A. arandae ), possessing thorny spinelets on the abactinal arm plates (lacking in A. arandae ), more weakly stellate body shape (R/r=3.5 versus>4.0 in A. arandae ), and much broader proximal arm width. Atheraster arandae from Madagascar and New Caledonia is found at similar depth, 1600–2160 m, to A. pheos n. sp., which occurs at 1852 m.

The significance of the smaller-sized interradial spination is unclear. Other deep-sea goniasterids with similar morphology have been observed in complex, acrobatic positions on octocoral prey, suggesting that interradial spines are related to arm flexure. Alternatively, spination on these plates may represent phenotypic variation relative to differing types of predators.

Occurrence . Australia. Gascoyne Marine Preserve , circa 273 km WNW of Low Point, Western Australia. 20º 48'08.1612'' S, 111º 36' 55.5984'' E, 1852 m .

Description. Body stout, strongly stellate (R/r=3.4), arms narrow, tapering, strongly upturned. Interradial arcs weakly curved to straight. Marginal plates lateral facing.

Abactinal surface composed of two sizes of plates, disk plates abutted, round to irregularly polygonal, distinctly smaller than those on arms. Central surface on disk plates smooth and bare with no accessories. Arm plates gradually intergrading with those on disk to become larger distally, each becoming approximately 2–3 times the overall size of plates on the disk region. Disk plates homogeneous in size, shape relative to those on arm, which are larger but also more heterogeneous in size and shape. Disk plates each with peripheral granules, quadrate in shape, 6–16 per plate, homogeneous in size, peripheral granules forming approximately 20% of the total plate diameter. Granular periphery in contact with other granules forming doubled granule around plates on the abactinal surface. Papulae single, present most abundantly around radial regions, absent from arm surface. Pedicellariae paddle-shaped, present on a minority of plates. Madreporite large, irregular in shape, mound-like, flanked by 6–7 adjacent abactinal plates.

Marginal plates, 27–30 per arm side, 54–60 per interradius (arm tip to arm tip). Marginal plates individually wide, predominantly with lateral-facing superomarginals forming narrow periphery when viewed from abactinal surface; inferomarginals prominent from actinal surface but not evident from abactinal surface. Superomarginal plate series most clearly quadrate in shape, with rounded abactinal-lateral angle distalmost on arm, plates interradially jumbled, arrangement irregular, some plates appearing fragmented and smaller than adjacent plates in series. Plates develop a more ordered and consistent appearance at arm base. Superomarginal plates with a pronounced armament, 6–10 short pointed spines, most strongly expressed interradially. More distally along arms 8–10 superomarginals away from the terminus, single, short thorn-like spines present on the plate surface. Superomarginals in the intervening distance along the arm with irregular alternation between single thorn-like spines and multiple smaller spines. Single large paddle-shaped pedicellaria present on a minority of superomarginal plates. Other than spines and pedicellariae, superomarginal plate surfaces are bare and smooth. Peripheral quadrate-shaped granules, 20–60, around superomarginal and inferomarginal plates. Inferomarginal plates with more pronounced facing on actinal surface. Surficial armament similar to that on superomarginal plates, irregularly alternating between six and ten spines proximally (especially interradially), becoming a single thorn-like spine distally along arm adjacent to terminus. Paddle-like pedicellariae on a minority of inferomarginal plates, but usually one per plate, especially numerous on those interradially. Inferomarginal plates similarly irregular in morphology and distribution interradially, with plate variability extending over midway along arm distance. A minority of superomarginal and inferomarginal plates distally along arm devoid of any armament, surface smooth. Spineless plates present distally on arms. Shallow fasciolar grooves present between superomarginal and actinal plates.

Actinal regions composed of two complete series, with irregular arrangement of plates adjacent to inferomarginal plate contact, these series limited to disk with no plates extending onto arms. Individual actinal plates weakly quadrate to irregularly polygonal in shape each with pointed granules, 5–20, widely spaced, present along each plate periphery. Most plates with broad paddle-shaped pedicellariae, each with valves bearing smooth to weakly developed “teeth”, four to five along top edge. Actinal plate surface otherwise bare and smooth. Shallow fasciolar grooves present.

Adambulacral plates quadrate in shape. Furrow spines, 6–9 in straight to weakly convex series. Spines blunt, quadrate in cross-section. Adjacent to furrow spines, a large paddle-shaped pedicellaria with rectangular valves and smooth edges. Remainder of adambulacral plate covered by a single series of four subambulacral spines, pointed but thick and quadrate in cross-section and relatively low, thick granules with pointed tips similar to peripheral granules on actinal plates. Oral plates with approximately 15 furrow spines, similar to those on the adambulacral plates, blunt and quadrate in cross-section. A larger spine, triangular in cross-section, pointed into mouth. Remainder of oral plate with an irregular number of short blunt spines, 2–4 per plate, and large rectangular pedicellariae, 1–4, identical to those on the adambulacral plates.

Material examined. Holotype. WAM Z110039 ( CSIRO barcode 10051582), Gascoyne Marine Preserve , circa 273 km WNW of Low Point, Western Australia. 20º 48'08.1612'' S, 111º 36'55.5984'' E, 2013 m, coll. RV Investigator, Gascoyne Expedition , 3 Dec 2022. 1 wet spec, R =11.6, r=3.4.