Evoplosoma besseyae, 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 : 16-18

Evoplosoma besseyae n. sp.

urn:lsid:zoobank.org:act:32A34022-126F-4EAE-867D-

3D981C46D136

Figure 7a–g

Etymology. This species is named for Dr Cindy Bessey, benthic ecologist at CSIRO, in honour of her contributions to our understanding of Australian marine ecology.

Diagnosis. Body shape stellate (R/r=3.19), arms elongate, disk distinctly pentagonal, interradial arcs weakly curved to straight. Abactinal plate surface covered by blocky granules. Prominent cone shaped spines and tubercles present on radial regions proximally on disk and arms. Marginal plates 50–52, lateral facing. Interradial plates with 3–5 prominent spines decreasing to two then a single spine, with none on distalmost marginal plates. Marginal plate surface covered by low, round granules, polygonal in shape. Actinal plate surface covered by similar granules, prominent conical spines and keyhole-shaped pedicellariae, valves lacking teeth. Furrow spines 2–4 (mostly four). Prominent elongate, paddle-shaped pedicellariae, each valve with 4–6 teeth.

Comments. This species is similar to E. tasmanica (McKnight 2006) in number of marginal plates per interradius, spines on both marginal plate series, and a covering of granules that extends over the abactinal, marginal and actinal plate surfaces. Although furrow spine number differs, it is similar– three to four (mostly four) versus 2–4 (mostly three) in E. tasmanica . Evoplosoma besseyae differs in the possession of well-developed abactinal conical spines, numerous interradial spines on the superomarginal and inferomarginal plates, larger, more abundant granules on abactinal, marginal and actinal surfaces, more elongate arms, four rather than three furrow spines, and actinal pedicellariae with differing morphology than those in E. tasmanica .

Polynoid associations? Based on collection notes, three commensal polynoid polychaetes were found in association with this specimen. In situ videos show deep-sea polynoid worms in association with Atlantic goniasterids such as Ceramaster and Nymphaster ( Mah, 2020) . Polynoids were also observed in association with Hippasteria during the CAPSTONE expedition and by the R/V Nautilus (Mah, unpublished data) in the tropical North Pacific, appearing to reside on the animal’s surface among the spines on the abactinal and marginal spines.

The precise relationship of the worms with NMV F122735 is unclear. Three polynoid specimen lots were collected from this station, including NMV F133659, NMV F133867, NMV F155868. NMV F133659 is a specimen of an apparently undescribed species of Brychionoe ( Polynoidae ), which is known currently from a single species, Brychionoe karenae Hanley & Burke 1991 , which was described from 1100 m off the east coast of Tasmania as a commensal on the antipatharian Leiopathes (R. Wilson, Museums Victoria, pers. comm.). Because the species is undescribed, it is unclear which host, if any, this worm lived with in association.

The remaining two specimens, NMV F133867 and NMV F155868 , were identified as a species in Macellicephala , which includes approximately 26 species ( R. Wilson, Museums Victoria, pers. comm). Relationships with asteroids are apparently unknown .

Occurrence . South of Tasmania, 1100–1273 m .

Description. Body strongly stellate (R/r=3.19), arms elongate, gradually tapering triangular with pointed arm tips. Interradial arcs weakly curved to straight.

Abactinal plates irregular to polygonal, abutted, infused in tissue, extending from disk to terminal plate. Surface completely covered by abundant blocky granules, polygonal to irregular in shape, in clusters of 1–5, with each cluster distinctly spaced from others, forming a distinct layer over the abactinal surface. Granular density more abundant adjacent to contact with superomarginal plates. Conical blunt tubercular spines present throughout the abactinal surface, especially along disk and radial regions, with few to none interradially. Each spine is flanked by 8–12 surface granules. Papulae elongate and tentacular, present only on disk and along radial regions. Spines most abundant on disk, proximally on arms, becoming fewer and then absent distally on arm adjacent to terminus. Madreporite round, oval to polygonal in shape, flanked by six plates. Pedicellariae absent.

Marginal plates, 50–52 per interradius (arm tip to arm tip), individually quadrate in shape, with rounded edges. Interradial marginal plates with distinct lateral facing becoming more dorsal facing along arms. Superomarginal and inferomarginal plate contact with more interradially, becoming more offset distally. Superomarginal series both with prominent spines, three to four (mostly three) distinct pointed cone-shaped spines on interradial plates, sitting on a raised base, and proximally along arms, decreasing to two and then a single distinct single conical spine distalmost along arms. Inferomarginal plates with four or five shorter but similar conical spines, with irregular round tubercles, then similarly decreasing to fewer or smaller spines distally. Marginal plate surface covered by granules, hemispherical, evenly spaced over plate surface interradially. Granules, coarse, 40–60, arranged around edge in peripheral series, then on surface around spines, 20–40. Damaged marginal plates show repair, with irregular plates present between superomarginal and inferomarginal series, and granules covering irregular plate surfaces.

Actinal plates in full series, chevron-like arrangement. A full actinal series extending along arm to terminus. Granules, 10–15 per plate, round, smooth, widely spaced, covering plate surface. Prominent tubercles and/or conical spines present on nearly every actinal plate, with smaller spines or tubercles present on actinal plates adjacent to the inferomarginal series. Pedicellariae keyhole/paddle-shaped with round edges, no teeth, present on approximately 50% of actinal plates.

Furrow spines, three or four (mostly four), unwebbed, round in cross-section, variably flattened, with blunt tips in straight to weakly palmate series. Adambulacral plate with prominent subambulacral spine, round in cross-section, approximately 2–3 times as thick as each furrow spine, set off from furrow spines by a distinct diastema. Proximally on adambulacral plate is a distinct paddle-like pedicellaria, similar in size to the subambulacral spine, with six teeth on each valve. A third, smaller subambulacral spine variably present adjacent or distal to the subambulacral spine and pedicellariae. Remainder of subambulacral plate surface with flat, rounded granules identical to those on actinal surface.

Oral plates with 10–11 flattened furrow spines with a single spine from each half projecting into mouth. Individual round, smooth granules, 8–10, present on either side of the diastema of the oral plates. Granules, 5–10, similar to those on the actinal surface, cover oral plate surfaces.

Material examined. Holotype. NMV F122735 41 km NE of Cape Tourville. 41.909° S, 148.752° E, 1273– 1190 m. 1 wet spec, R =11.5, r=3.6.

Paratype. NMV F159243 ° S of Tasmania, Hill U Site, Southern Ocean. 44.3257° S, 147.175° E, 1100–1160 m, Coll . T. O’Hara & T. Costa 2 April 2007 , R / V Southern Surveyor. 1 wet spec , R=8.2, r=2.4.