Astrotholus infernalis Mah 2023, n. gen.

Astrotholus infernalis n. gen. n. sp.

FIGURE 2A–F

Hurtado-Garcia & Manjón-Cabeza 2022: 1220 (as Anseropoda antarctica)

Etymology

The species epithet “ infernalis ” describing “lower regions” and alluding to the great depth occurrence of this species.

Diagnosis

Body pentagonal to weakly stellate (R/r=1.3–2.5, but mostly between 1.4–1.6), arms triangular, disk arched, actinal surface concave, interradial arcs weakly curved to straight (Fig. 2A). Abactinal plates imbricate, flat to mound-like or arched (Fig. 2C). Abactinal plate surfaces each covered with spinelets, 4–20, mostly 5–10, widely spaced (Fig. 2B). Spinelet tips hyaline, 3–4. Marginal plates 30 to 38 to 40 (at R=1.0, R=1.2 to R=1.6 respectively) per interradius (arm tip to arm tip), imbricate. Superomarginal plates oval to quadrate in shape (Fig. 2C), plate surface with 5–12 spinelets bearing minute hyaline tips, 3–4 identical to those of abactinal plates. Inferomarginal plates approximately 50% the size of the superomarginal plates, quadrate in outline. Surface covered with 1–5 spinelets bearing minute hyaline tips, 3–4 identical to those on superomarginals and abactinal plates. Actinal plates imbricate, in 30–40 transverse rows showing direct continuity with inferomarginal and adambulacral plates (Fig. 2E). Plates round but elongate, each with sharp, elongate spines, 2–4 per plate (Fig. 2D, E, F).

Furrow spines elongate with pointed tips, webbed (sometimes torn) 2 to 4 in palmate to straight series, subambulacral spines identically elongate with pointed tips and webbed, 2 to 4 per plate, set off from the furrow spine by a discrete space (Fig. 2F).

Comments

Astrotholus infernalis n. gen. n. sp. represents the deepest known member of the Asterinidae with collection from 3788–3944 m. Specimen USNM 1122403, the holotype of this species was cited as part of “ Anseropoda antarctica ” by Hurtado-Garcia & Manjón-Cabeza (2022)

Occurrence Georgia Island, Elephant Island, Scotia Sea, South Atlantic, Tierra del Fuego. 1000–3944 m.

Description

Body pentagonal to weakly stellate (R/r=1.3–2.5, but mostly between 1.4–1.6), arms triangular, disk arched, actinal surface concave, interradial arcs weakly curved to straight (Fig. 2A).

Abactinal plates imbricate, most scalar, irregularly rounded most showing smooth, flat surface others are more mound-like (Fig. 2A, C). Grooves arising as a result of adjacent mound-like plates. Plates largest on proximal region on disk and along radial regions of arms. Interradial plates more elongate in shape, arranged in transverse, ordered series with variably direct or slightly offset correspondence to superomarginal plates. Abactinal plate surfaces each covered with spinelets, 4–50, mostly 10–30, but number related to plate size. Spinelets cover each plate surface, closely but evenly spaced. Each spinelet with minute hyaline tips, 3–4. Madreporite triangular with deep sulci. Anus centrally located on disk, flanked by 4–6 plates, protected by overlying spinelets.

Marginal plates 30 to 38 to 40 (at R=1.0, R=1.2 to R=1.6 respectively) per interradius (arm tip to arm tip). Superomarginal plates with 1:1 correspondence with inferomarginal plates. Superomarginal plates imbricate, shape ovoid to quadrate with rounded corners, variably offset or directly in association with serially arranged transverse, interradial abactinal plates (Fig. 2C). Superomarginal plate surfaces with 5–12 spinelets bearing minute hyaline tips, 3–4 identical to those present on abactinal plates. Inferomarginal plates approximately 50% the size of the superomarginal plates, quadrate in outline. Surface covered with 5–12 spinelets bearing minute hyaline tips, 3–4 identical to those on superomarginals and abactinal plates. The convex outline of the superomarginal and inferomarginal plates forms a crenulated online along the lateral edge of the body (Fig. 2C). Shallow groove present at contact between superomarginal and inferomarginal plate series. Terminal plate quadrate in outline, smooth with no accessories (no spines, granules, etc.) (Fig. 2C).

Actinal plates imbricate, in 30–40 transverse rows in direct association with inferomarginal and adambulacral plates. Plates round but elongate, each with sharp, elongate spines, 2–4 per plate (Fig. 2D, E, F).

Furrow spines, elongate with pointed tip, webbed (sometimes torn), 2–4 in palmate to straight series, subambulacral spines identically elongate with pointed tips and webbed, 2–4 per plate, set off from the furrow spine by a discrete space (Fig. 2D, F). Greatest number of furrow spines proximally with distalmost adambulacral plate showing fewest spines. Oral plates with furrow spines 5–12 at R=0.9 to R=1.5. At R=0.9, the paired oral spines projecting into the mouth are enlarged, approximately twice the length of the other oral plate furrow spines. Oral plates with pronounced ridge and enlarged central fissure between paired plates (Fig. 2D).