Circeaster dux, 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 : 13-15

Circeaster dux n.sp.

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Figure 6a–h

Etymology. The specific epithet dux is Latin for “commander” or “leader”, alluding to this species’ striking appearance.

Diagnosis. Body stellate (R/r=3.06), arms elongate, triangular. Body covered by hemispherical granules, spinelets absent. Abactinal plates flat to weakly convex, bare other than pedicellariae. Large abactinal plates on arms, strongly tumid, in 4–6 series, arm plates at least twice as large as those on disk. Superomarginal plates forming distinct frame when viewed dorsally. Marginal plate lateral surface with 2–4 paddle-shaped alveolar pedicellariae; three or more present interradially, decreasing to two or fewer distally. Marginal plates smooth and bare, save for flattened, round granules, 20–30 on abactinal surface of superomarginals, lower surface of inferomarginals. Furrow spines 6–8, triangular in cross-section. Subambulacrals three, with jagged, broad tips, each approximately twice as thick as the adjacent furrow spine. Each adambulacral plate with a large clam-like pedicellaria similar to those on abactinal surface with four jagged, well-spaced teeth on each valve.

Comments. This species resembles Circeaster kristinae Mah 2006 and Circeaster magdalenae Koehler 1909 : all share a similar arm and disk shape, prominent superomarginal frame, and similar abactinal plates when viewed on the abactinal surface. It differs in lacking a spinelet-covered surface, and is instead covered by numerous smooth, hemispherical granules. Granules are present in abundance on the abactinal arm plates, but sparingly present on C. kristinae and C. magdalenae . Three subambulacral spines are present in Circeaster n sp., whereas only one or two are present in C. kristinae and none occur on C. magdalenae .

Most distinctive about this species is the numerous alveolar pedicellariae on the surface of both superomarginal and inferomarginal plates in regular series.

Occurrence . Known only from the type locality, Site 30 Gascoyne Marine Park , 19 km W. of Lakeside , Western Australia, 22.00276° S, 113.733333° E, 713 m.

Description. Body stout, thickened, strongly stellate (R/r=3.06), arms triangular, elongate, proximally wide narrowing at arm tip. Interradial arcs weakly curved to straight.

Abactinal surface mostly flat on disk, many strongly convex plates on arms. Plates on arms gradually transition to larger and differing from those on disk. Disk plates round to polygonal in shape, each with 1–30 widely separated, coarse, deciduous granules. Plates on disk with many granules and pedicellariae. Pedicellariae paddle-shaped, valves thin, each with 7–10 teeth, present on approximately 40% of plates, with greatest occurrence proximally, especially along papular and other proximal regions. Interradial regions, adjacent to superomarginal contact with plates smaller bearing fewer (1–3) granules, and no pedicellariae. Abactinal arm plates at base wider and larger, 1–3 times the width of proximal disk plates. Disk plates adjacent to the arms similar in size to basal arm plates. Carinal and adradials along arm acutely convex with greater numbers of granules, each bearing up to 25 at arm midpoint. Granules begin to disappear 8–10 superomarginals away from arm tip. Plates flat, surfaces bare and smooth. Abactinal plates along arm decrease at this point from three or four at arm base to a single series adjacent to arm tip. Distalmost superomarginal plates abutted approximately three superomarginals from arm tip. Madreporite hexagonal, convex, rising above body surface with strongly developed sulci, flanked by eight plates. Anus not evident.

Marginal plates, approximately 27–30 per arm side (full interradius 54–60, arm tip to arm tip). All marginal plates with quadrate granules, approximately 15–20 per side, 60–80 surrounding the plate periphery of each. Superomarginal and inferomarginal plates with strong 1:1 association in each interradius showing associated plates to arm tip. Lateral edge rolled, showing not just the superomarginal but the inferomarginal plate surface from dorsal view. Superomarginal plates wide, quadrate in shape, with rounded edges. Superomarginal abactinal-lateral edge round; plate in cross-section is mound-like. Superomarginal surface with 1–35 widely spaced coarse granules, mostly 20–25 on superomarginal plate surface, in addition to 1–3 clam-shell pedicellariae, identical to those on the abactinal surface. Granule and pedicellariae abundance greatest interradially, decreasing from 35 proximally to a single or absent granule or near arm tip. Inferomarginal plates with identical types of granules and pedicellariae but in greater numbers (up to 50), decreasing to none on inferomarginal adjacent to arm tip. Inferomarginal pedicellariae, 1–8, greatest number interradially. Approximately half positioned at upper end of inferomarginal plate, other half on inferomarginal plate surface adjacent to actinal plate contact. Distalmost superomarginal plates abutted, with no granules, pedicellariae on surface. Terminal plates triangular to conical in shape.

Actinal region large with six or seven full series in chevron formation, with remainder adjacent to inferomarginal plates in irregular formation. Individual plates quadrate to irregular in shape. Each actinal plate with a peripheral ring of 10–30 (mostly 20–25) widely spaced angular, quadrate granules. A large clam shell-shaped pedicellaria with multiple valves is present at the centre of nearly all actinal plates.

Furrow spines 6–8, decreasing in number proximally to distally. Spines are pointed, with jagged tips, angular to triangular in cross-section, arranged in concave arc. Subambulacrals three, with jagged, broad tips, each approximately twice as thick as the adjacent furrow spine. Each adambulacral plate has a large clam-like pedicellaria similar to those on the abactinal surface, with four jagged, well-spaced teeth on each valve. Further subambulacral spination/granules on adambulacral plate similar in shape and size to granules on actinal plate surface.

Oral plates with 10–15 furrow spines in straight series, each with jagged, denticulate tips, quadrate in cross-section, each triangular to quadrate in cross-section, similar to those on adambulacral furrow spines. Granules, 10, paired, molar-shaped, along either side of the diastema between the paired oral plates. Irregular array of flattened quadrate, angular granules present on oral plate and adjacent areas.

Material examined. Holotype. WAM Z110163 ( CSIRO barcode 10055627), Site 30 Gascoyne Marine Park, 19 km W. Lakeside, Western Australia. 22.00276° S, 113.733333° E, 794 m, coll. RV Investigator , 8 Dec. 2022. 1 wet spec, R =13.2 r= 4.3 cm.