Astrotholus mei, Mah, 2023

Mah, Christopher L., 2023, New Genera, Species, and observations on the biology of Antarctic Valvatida (Asteroidea), Zootaxa 5310 (1), pp. 1-88 : 15-17

Astrotholus mei n. gen. n. sp.

FIGURE 3A–F

Etymology

This species is named in the memory of Mei Elizabeth Sato (2006–2021), daughter of colleague Anouchka Krygelmans, formerly of the Muséum national d’Histoire naturelle. Species name, noun held in apposition.

Diagnosis

Body weakly stellate, with size up to R= 2.4. Spines, 6 to 30, clavate on subpaxillate abactinal plates ( Fig. 3A ). Superomarginals and inferomarginals similar in size ( Fig. 3E ). Actinal spines elongate, one to two per plate, mostly one. Furrow spines 2 to 5, proximally 3 to 4 webbed with a distinct transverse series of webbed subambulacral spines, 2 to 3 set off from the furrow by a distinct space ( Fig. 3F ).

Comments

Of the Astrotholus spp. Astrotholus mei n. gen. n. sp. displayed the largest and most robust individuals with largest size at R= 2.4 cm demonstrating a correspondingly thick disk. Despite its massive appearance and differing number and shape of its actinal spines this species shares several character similarities with Astrotholus antarcticus , in displaying more granuliform spinelets and mound-like abactinal plates.

Occurrence

Scotia Sea , off South Georgia Island, −55.092, −39.842, 2886–3040 m .

Description

Body weakly stellate (R/r=1.4–2.0 at R=0.8, but mostly 1.4–1.5), disk thick, strongly arched, actinal surface concave, interradial arcs weakly curved to straight ( Fig. 3A ). Body surface with a distinct dermal layer underlying spaces between plates.

Abactinal plates imbricate, subpaxillate, each plate topped by densely arranged short, club-tipped spinelets with very minute micro-spinelets (barely visible without a microscope). Spinelets, six to 50 at R=2.3 ( Fig. 3B ). Spinelet count appears size dependent with smaller plates having fewest number; largest plates with greatest spinelet number. Individually plates are irregular to polygonal in outline, with a pronounced central mound becoming simpler and more found distally adjacent to superomarginals. Radial plates along arm, two to four, each with low, irregular mound-like shape ranging from weakly arched to more bump-like. Plates smaller with more quadrate to polygonal shapes distally becoming larger and more irregular in shape centrally on disk. Distinct, well-developed grooves present between abactinal plates. Madreporite round to polygonal, flanked by six to eight abactinal plates. Papulae single, present in circular region at arm base. Anus flanked by four plates, obscured by spinelets.

Marginal plates 60 per interradius (arm tip to arm tip) at R=2.1, superomarginals and inferomarginals with 1:1 correspondence, most in parallel to one another but plates more distally sitting at oblique angles ( Fig. 3E ). Superomarginals and inferomarginals each covered by club-shaped spinelets identical to those on abactinal plates, 12–20 each. Superomarginals and inferomarginals similar in overall size, strongly convex, round plates in each series separated by a discrete space forming a weakly crenulate outline. Superomarginals and inferomarginals separated by a distinct furrow. Superomarginals part of direct series with interradial plate series, inferomarginals show identical correspondence with actinal plate series. Terminal plate pentagonal, toe shaped, bare and smooth with no spines or other accessories.

Actinal intermediate regions composed of plates, imbricate, in linear series, elongate to round ( Fig. 3C, D. F ). Actinal surface covered with a distinct dermal layer which is observed between plate series. Approximately 30 linear series (15 per arm) in each interradius (at R=2.0), in direct association with inferomarginal plates. Most plates with a single, large blunt spine with spinelets on the tip of each. Actinal spines present centrally on each plate with a proximal most actinal plate armed with two spines. Spines extend well above the plane of the actinal surface, approximately 1.0–2.0 mm in length.

Furrow spines webbed, 2 to 5, largest number proximally, decreasing to two adjacent to arm tip ( Fig. 3D, F ). Furrow spines longest centrally with shortest spines on either side. Subambulacral spines two to three, set off from furrow spines by discrete space. Both subambulacral and actinal spines identical in size, stature. Both with small microspinelets on tip. Oral plate furrow spines webbed, nine forming distinct “fence” around oral plates in oral region. Oral plates each with two oral spines, totaling four in each radius. Oral plates with distinctly convex surface and well-developed tissue covered fissure between them.

Material Examined

Holotype. USNM 1662082 , South Georgia Island, Scotia Sea, South Atlantic Ocean , −55.092, −39.842, 2886– 3040 m. Coll. R/V Eltanin, 8 Feb. 1966. 1 dry spec. R=2.3 r=1.5.

Paratypes. USNM 1122325 , South Georgia Island, Scotia Sea, South Atlantic Ocean , −55.092, −39.842, 2886– 3040 m. Coll. R/V Eltanin, 8 Feb. 1966. 44 dry specs. R=0.8 r=0.4, R=1.0 r=0.6, R=1.0 r=0.6, R=1.2 r=0.7, R=1.1 r=0.7, R=1.1 r =0.7, R=1.2 r=0.7, R=1.4 r=0.7, R=1.2 r=0.9, R=1.6 r=1.0, R=1.4 r=1.0, R=1.4 r=0.9, R=1.4 r=0.9 (broken specimen), R=1.6 r=0.9, R=1.7 r=1.1, R=1.7 r=1.3, R=1.9 r=1.1, R=1.0 r=0.7, R=1.9 r=1.1, R=1.7 r=0.9. R=1.9 r=1.2, R=1.9 r=1.1, R=1.7 r=1.2, R=1.7 r=1.1, R=1.7 r=1.2, R=1.6 r=1.1, R=1.5 r=0.9, R=1.3 r=1.0, R=1.6 r=1.0, R=1.6 r=1.0, R=1.7 r=1.1, R=1.4 r=0.9, R=1.6 r=1.2, R=1.5 r=1.0, R=1.9 r=1.3, R=1.7 r=1.2, R=1.7 r=1.1, R=1.7 r=1.3, R=1.9 r=1.2, R=1.9 r=1.3, R=1.9 r=1.3, R=2.0 r=1.3, R=2.1 r=1.5, R=2.3 r=1.5, R=2.0 r=1.3, R=2.4 r=1.7.

USNM 1573482 , Scotia Sea, South Georgia Island, Scotia Sea, South Atlantic Ocean , −56.875, −37.542, 3138– 3144 m. Coll. R/V Eltanin, 28 Aug. 1963. 2 dry spec. R=1.3 r=0.8, R=2.3 r=1.6.

USNM 1573487 , South of South Georgia Island, Scotia Sea, South Atlantic Ocean , −56.25, −38.567, 2869– 3038 m. Coll. R/V Eltanin, 9 March 1966. 6 dry specs. R=1.3 r=0.9, R=1.7 r=1.0, R=1.4 r=0.8, R=1.9 r=1.5, R=2.3 r=1.8, R=1.6 r=1.3.

USNM 1664398 , South Georgia Island, Scotia Sea, South Atlantic Ocean , −55.092, −39.842, 2886–3040 m. Coll. R/V Eltanin, 8 Feb. 1966.1 dry spec. R=2.1 r=1.2.

USNM 1664401 , South of South Georgia Island, Scotia Sea, South Atlantic Ocean . −56.25, −38.567, 2869– 3038 m. Coll. R/V Eltanin, 9 March 1966. 2 dry specs. R=1.4 r=0.9, R=1.4 r=1.0.

CASIZ 163122 , Shackleton Fracture Zone, −59.396667, −60.065, 2201–2213 m. Coll. R. Mooi & S. Lockhart, PFS Polarstern, 27 Jan. 2002. 2 wet specs. R=0.7 r=0.4, R=0.6 r=0.3.

Figures

FIGURE 3. Astrotholus mei n. gen. n. sp. USNM 1662082 Holotype. A. Abactinal surface. B. Close up of abactinal granules. C. Oral surface. D. Oral surface showing mouth, actinal and furrow spines. E. Lateral view showing abactinal granules, superomarginal and inferomarginal plates. F. Close-up of furrow and actinal spines.