Atheraster umbo, 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 : 10-13

Atheraster umbo n. sp.

urn:lsid:zoobank.org:act:049A6DE1-0722-4252-A363-

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Figures 4a–f, 5a–f

Etymology. The species epithet, umbo , is Latin for a boss or swelling, alluding to the tumescent projections present on the marginal plates.

Diagnosis. Body stout, strongly stellate (R/r=3.2), arms elongate, triangular, interradial arcs weakly curved to straight. Abactinal plates irregular, bare, extending to arm tip. Arm plates variably flat to strongly convex, acutely large relative to adjacent disk plates. Pedicellariae abundant, 4–12, along depression in each interradius. Five plates across proximally on arms decreasing to a single series to terminus. Marginal plates, 40–44 per interradius, 20–22 per arm side, interradially with 2–10 small granules/tubercles, but otherwise smooth and bare. Marginal plates along the arms with single distinct tumescence. Granules coarse, nearly tubercular, most abundant (1–15) interradially on marginal plates, decreasing then absent along arm surface. Actinal plates with distinct alveolar pedicellariae flanked on either side by bisected hemispherical granules. Furrow spines 5–15, but mostly seven or eight, with a prominent single tong-like pedicellaria with quadrate valves on each adambulacral plate. Spine, large thick, 2–3 times the thickness of the furrow spines, identical in length to the longest of the furrow spines, present at oblique angle to pedicellariae. Oral plates, each with large, paddle-shaped pedicellaria per plate, thus two per interradius, but not symmetrically positioned.

Comments. Although lacking well-developed spines, the tumescent structures on the marginal plates display a strongly arched shape and pattern that appears very similar to spines in other Atheraster species. This species’ marginal plate ornamentation pattern parallels A. pheos n. sp. in showing interradial superomarginal plates with 2–10 minute surficial accessory structures (i.e. granules/tubercles) relative to the larger, single arched tumescence present on superomarginal arm plates present on each arm. Atheraster pheos also displays many small spines, 6–10 on each interradial superomarginal, which are succeeded by a single conical spine on each superomarginal plate along the arm.

The three type specimens, which were collected from distinctly different localities (the Cocos/Keeling Islands and Tasmanian/southeast Pacific), show the same arched or tumescent marginal plates. Additional specimens could show these to be damaged or be some sort of incipient spine, but examination of material on hand suggests they are a diagnostic character of this distinct species.

This species invites comparison with two Pacific Circeaster species, C. sandrae Mah 2006 and C. pullus Mah 2006 . Atheraster umbo n. sp. differs in lacking any granulation on the marginal plates surface, displaying large strongly convex abactinal arm plate and in showing a large number of abactinal granules around the madreporite.

Although no direct association was observed, the New Caledonia specimen, IE-2013-7118, was collected from a station that also included members of the Isididae (bamboo corals), which goniasterid predators feed upon frequently.

Occurrence . Cocos (Keeling) Islands Territory, Indian Ocean, Australia, Lord Howe Rise, Southeast Cape, Tasmania, New Caledonia 1896– 1589 m.

Description. Body stout, strongly stellate (R/r=2.1–3.2), arms elongate, triangular, interradial arcs weakly curved to straight.

Abactinal surface, weakly arched, plates abutted, polygonal, extending from disk to arm tip. Arm and disk plates round to irregularly polygonal in shape but relatively similar in size. The holotype, from Ningaloo, has arm plates only slightly larger than those on disk with gradual transition, but a minority of arm plates, variably 1–4 per arm, are strongly convex, rising well above the body surface. Tasmanian specimens show arm plates up to three or four times the size of disk plates, most arm plates with strongly convex surface, appearing nearly hemispherical. Arm plate surfaces all smooth, devoid of granules with gradually decreasing number of abactinal plates, 3–5 at arm base, decreasing to a single row adjacent to the terminus. Superomarginals with two or three pairs abutted at arm tip on the Tasmanian specimens, but plates continue to terminus on the Ningaloo specimen. Disk plates mostly bare save for dense aggregation of granules surrounding the madreporite. Pedicellariae present in abundance on the Ningaloo specimen, but largely absent from the surface of the Tasmanian ones. Paddle-shaped pedicellariae with flat, round valves present on a minority of disk plates, each pedicellaria within a distinct alveolus or pit. Pedicellariae are most abundant, 4–12, in a distinct valley-like depression present in each interradius. Each plate surrounded by 9–30 polygonal to quadrate granules in close-set series. Each abactinal plate central region flat to weakly concave. Madreporite convex, round in shape with well-developed sulci. Surrounding region with large, coarse granules, 1–12 per plate.

Marginal plates, 40–44 (20–22 along each arm), present in each interradius (arm tip to arm tip, forming a wide boundary around body periphery. Interradial marginal plates with a laterally-directed facing becoming more dorsal facing along arms. Disk superomarginal plates bare, smooth save for 2–10, distinct, spherical granules or tubercles, leaving concave pitting on surface, centrally present on each interradial plate. Ornamentation on superomarginal plate surface along arm with a single distinct tumescence, variably arched with a tip becoming more rounded distally, forming a distinctly crenulated periphery along the arm. Pedicellariae alveolar, 1–4, tong-like with triangular blades on marginal plate surface. Superomarginal plate surface weakly concave, no granules on superomarginal plate surface. Each superomarginal plate with a rounded edge, each plate round in cross-section. Marginal plates with 40–100 peripheral granules, quadrate to polygonal. Inferomarginals with 1–20 distinct, coarse granules, highest interradially, with 10–15 on central inferomarginal plate surfaces decreasing to a single granule at arm base. Pedicellariae, 1–6, mostly 3–4, alveolar with triangular valves decreasing distally and absent along arms.

Actinal plates in three full series arranged in chevrons, individual plates, irregularly polygonal to round. Each plate with distinctly large, alveolar, paddle-shaped pedicellariae, approximately 1.0 mm in length with quadrate tips, flanked on either side of paired valves by bisected hemispherical granules. Single actinal plate series continues to proximal arm region, where it ends. Actinal plates covered by large round tubercles, coarse granules abundant, closely arranged adjacent to inferomarginal plates. Each actinal plate with coarse granules, 6 to 15 present around periphery.

Furrow spines 5–8, quadrate in cross-section with rounded tips. Furrow spines 12–15 on adambulacral plate adjacent to the oral plate, these furrow spines flattened to spatulate with quadrate-shaped tips. Most adambulacral plates have a prominent, alveolar, paddle-shaped pedicellaria. Remaining surface of each adambulacral surface with a single, large blunt spine on distal side of plate, this spine 2–3 times the width of the furrow spines, extending to approximate height of tallest furrow spine. One to five thick subambulacral spines, short to granular in size on remainder of plate, but especially on side in contact with actinal plates.

Oral plates, each with a large, paddle-shaped pedicellaria approximately 2.0 mm in length, thus two per interradius but unevenly present per interradius. Furrow spines on oral plates, 18–25, closely arranged, each flattened with tallest plates projecting into mouth. Each oral plate with 8–10 granular spines with angular tips, quadrate to polygonal in cross-section, along the central fossae on the side of each plate. Peripheral oral plate with 5–7 angular granular spines along edge adjacent to contact with adambulacral plates.

Material examined. Holotype. NMV F307974 Cocos (Keeling) Islands Territory , Indian Ocean, Australia. 11.832222° S, 96.626667° E, 1896– 1589 m. Coll. Tim O’Hara et al. aboard RV Investigator , IN 2022 V08 IOT 2, Marine Invertebrates Team, 14–15 Oct 2022. 1 wet spec, R =7.7, r=2.4

Paratypes. NMV F 84959. 84 km SSE of South East Cape, Tasmania on J1 seamount. 44.27° S, 147.33° E, 1300–1450 m, coll . T.N. Stranks CSIRO, R / V Southern Surveyor. 27 Jan 1997. 1 wet spec , R=6.2, r=2.0.

NMV F159690 Lord Howe Rise , 27.4136833333° S, 161.70035° E, 1532 m. Coll. Geoscience Australia aboard R / V Tangaroa , 17 Oct 2007. 1 wet spec , R=3.9, r=1.8.

MNHN IE-2013-7118 New Caledonia, 23º 1.7'S, 168º 9.3' E, 1373– 1407 m. Coll. KANADEEP 2, CP 5108. 1 wet spec , R=5.3, r=1.6.