Astrosarkus, Mah, 2003

Mah, Christopher L., 2023, A new species of Astrosarkus from Western Australia including new Mesophotic occurrences of Indian Ocean Oreasteridae (Valvatida, Asteroidea), Memoirs of Museum Victoria 82, pp. 143-165 : 148-150

Astrosarkus lu nov. sp.

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Etymology. This species is named for Dr. Chung-Cheng Lu, curator emeritus at the Museum Victoria, who collected the specimen, in honour of his contribution to Australian invertebrate zoology. The surname Lu is held in apposition.

Diagnosis. Large pointed tubercles on the abactinal and lateral surface. Furrow spines thick, 4–7; subambulacral spines mostly 5–6, quadrate to round in cross-section in irregular series, each three times as thick as the furrow spines. Region adjacent to the adambulacral spination with numerous, relatively short bivalve pedicellariae.

Comments. This is the first specimen occurrence of Astrosarkus in Australia and as with A. idipi , Astrosarkus lu n. sp. occurs at mesophotic depths. This species shows small, thorn-like spines on the abactinal and lateral surfaces, as well as having differing numbers of adambulacral armaments, notably fewer furrow spines, 4–7 rather than 10–11 as in A. idipi , as well as having much larger and differently shaped subambulacral spines. These suggest a defensive function that might not apply to the more widespread A. idipi . Pedicellariae in A. lu n. sp. are similar in appearance but differ in having more elongate valves than A. idipi . Although a dissection of the holotype was not attempted, the fleshy material composing the body wall appears identical to the one present in A. idipi .

Although deck shots of this species were taken, colour was difficult to interpret, but appeared red to magenta on the abactinal surface with a white or light actinal surface. Other images of other Astrosarkus spp. studied herein showed no individuals with comparable colour or spination.

Occurrence. Off Western Australia in the Timor Sea , 83–84 m.

Description. Body pentagonal (R/r=1.25) thick (height= 5.5 cm), stout, covered in smooth flesh which obscures all but adambulacral spination and abactinal tubercular spines. Body solid to the touch, with flesh pushed unevenly on surface. Arm terminus upturned.

Abactinal surface forming a reticulated pattern composed of smooth granule-infused dermis and large distinct papular regions, 100–1000 papulae per area (approximately 1–2 cm x 1–2 cm). Papular regions vary in size and extend onto lateral surface, with largest areas along peripheral disk region adjacent to periphery. Smaller, more discrete regions present more centrally on disk and arms. Distinct elongate papulae emerge from about half of papular pores examined. Nonpapular regions composed of dense granule-infused dermis with approximately five granules on a 1.0 mm count. Single tubercular spines with pointed tips, interspersed throughout abactinal and lateral surfaces, most of these present on nonpapular surface but with some papular pore regions bearing a single spine. Madreporite round, polygonal, sitting on raised area on abactinal surface, base surrounded by tissue. Sulci relatively shallow.

Marginal plates not evident from external surface but covered by thick tissue. Lateral surface appears to be distinguished by weakly expressed elongate segments, approximately 14 per interradius. Each segment covered with a similarly elongate papular region, containing 500–1000 papulae on each. Tubercle-like spines present along lateral surface with regular occurrence on both papular and nonpapular areas. Terminal plate pronounced, triangular with rounded edges. Ambulacral grooves distinctly present along lateral surfaces on each radii.

Actinal surface demarcated by absence of papular regions, ostensibly beginning at lower end of marginal “segments” on lateral surface. Actinal intermediate area dominated by granule-infused dermis. Actinal–lateral areas relatively texture free but approaching midway to proximally, these areas have shallow grooves in addition to distinct valleys and dendritic indentions within each actinal intermediate region.

Furrow spines 4–7, mostly five or six, each spine blunt, thick, quadrate in cross-section with each array in straight to weakly concave formation. Subambulacral spines in two irregular rows, the one adjacent to furrow spines composed of two to three blunt spines each approximately three times the thickness of a furrow spine, the one proximal to the mouth with tapered tips, almost acorn-like in shape, these becoming more cylindrical in cross-section distally adjacent to the terminus. The second subambulacral spine mostly single but exceptionally with two, both of these adjacent to the actinal intermediate region. Region adjacent to the adambulacral spination with numerous, relatively small bivalve pedicellariae, approximately 1.0 mm in length, approximately 6–10 associated with each subambulacral spine. Coarse, larger quadrate to polygonal granules present, approximately three counted along a 1.0 mm line.

Oral plates with closely appressed furrow spines, nine per side, each with rounded, blunt tip, quadrate to round in cross-section, with some spines twice as thick as others. A single spine observed on the oral plate projecting into the mouth. Oral plate “surface” covered with irregularly large and thick spines, 10–15, similar in stature to subambulacrals but also irregular in size, shape, all closely appressed to one another. Actinal intermediate regions adjacent to adambulacral furrow spination with higher numbers of pedicellariae and greater numbers of larger granules.

Material described. Holotype, NMV F 242065 Australia, Western Australia, Timor Sea, North West Shelf , 12º 05' 12" S – 12º 54' S, 125º 37' E – 125º 35' E. 83–84 m. Coll. Chung Chen Lu. 1 April 1981. RV Hai Kung, Cruise number 70040102. 1 wet spec. R =16.5, r=~13.2, h=~ 5.5 cm (measured from underside).