Astrotholus, Mah, 2023

Mah, Christopher L., 2023, New Genera, Species, and observations on the biology of Antarctic Valvatida (Asteroidea), Zootaxa 5310 (1), pp. 1-88 : 9-10

Astrotholus nov. gen.

Etymology

The genus is a combination of astro for star and the Latin tholus for dome, which alludes to the strongly arched, convex shape present in this genus.

Diagnosis

Body form pentagonal to stellate, arms short, disk large. Disk strongly arched, interradial body wall thin. Actinal surface concave. Abactinal plates imbricate, variably flat to subpaxillate, rounded to elongate in shape. Plates with spinelets, variably thorn like, tips glassine to blunt and strongly club-like or granuliform in shape. These accessories showing association with underlying plates. Abactinal disk plates irregularly arranged on disk and arm radii but present in ordered series interradially between radial disk plates and superomarginals. Marginal plates small, forming crenulate lateral boundary between abactinal and actinal surface. Actinal intermediate plate region in linear rows showing association between inferomarginals and adambulacral plates. Actinal plate surface bare or in some taxa with single to multiple spinelets. Furrow spines webbed, numbering 3 to 6.

Type species: Astrotholus mei n. gen, n. sp.

Comments

This genus accommodates “ Anseropoda ” antarctica and the four new species reported herein, which had fallen under the broad range of the description for “ Anseropoda ” antarctica . The type species, described by Fisher (1940) from Clarence Island was collected from relatively shallow depth (311–426 m) compared to the species reported here which were collected from between 1000 and 4000 m except for Astrotholus phasma n. gen, n. sp. from 339– 494 m.

Included Species: Astrotholus antarcticus ( Fisher, 1940) , Astrotholus infernalis n. gen. n. sp. Astrotholus mei n. gen, n. sp. Astrotholus molginos n. gen. n. sp. Astrotholus phasma n. gen. n. sp.

Type species: Astrotholus mei n. sp.

Key to the species of Astrotholus n. gen.

(0) Surface with strongly convex or subpaxillate abactinal plates with multiple spinelets, each adorned with microspinelets or club-shaped tips.......................................................................................... (3)

(0’) Surface flat with single point spines or granules directly present on surface of each imbricate abactinal plate............ (1)

(1) Granules or granular spines (i.e., granules rounded, variably short and squat to more cylindrical interradially) on abactinal plates, ranging from 5 to 18. Actinal plates with spinelets, 3 to 6 per plate. Superomarginals approximately twice the size of the inferomarginals. Known depth range: 229– 426 m .............. Astrotholus antarcticus ........... nov. gen. nov. comb.

(1’) Abactinal plates with spines (pointed) ranging from 5 to 50 (mostly 15–30). Actinal plates, 1–2 in all but A. phasma , which can have up to 4 per plate. Superomarginals similar in size to inferomarginals. Depth range of A. phasma 339–528, but others, ranging from 2886–3944 m ............................................................................. (2)

(2) Superomarginal plates similar in size/width to inferomarginals. Single series of pointed spines, 1 to 8, along non-overlapping abactinal plate. Known depth range: 2886–3876 m ............................... Astrotholus molginos n. gen. n. sp.

(2’) Superomarginal plates twice as large as inferomarginals. Spinelets present around complete periphery of plate with central surface devoid of spination. Depth range: 339– 528 m ............................. Astrotholus phasma n. gen, n. sp.

(3) Abactinal plates strongly subpaxillate (i.e., forming a well-developed mound or convex surface) each with 6 to 30 (mostly 10–15) blunt, closely arranged, club-shaped spines, these at R=1.0 to 2.5 ( Fig. 3A, B, E ). Single papular pores present along radial regions. Larger individuals (R=2.5) with mound-shaped, thickened bodies, arms indistinct. Actinal plates with a stout, elongate spine, mostly single but a minority of plates with two spines, these rising well above the surface of the plate ( Fig. 2D, F ). Depth range of known specimens: 2886–3040..................................... Astrotholus mei n. gen, n. sp.

(3’) Abactinal plates flat to weakly subpaxillate with spinelets mostly 4–20, mostly 5–15, widely spaced. Spinelet tips rough, hyaline, 3–4. at R=~1.5, with each angular spinelet each displaying 3–4 hyaline tips. Larger individuals (R=1.5–1.7) arms more distinctly triangular in shape. Actinal plates with 2 to 4 fine widely spaced spines. Known depth range: 3788–3944 m ............................................................................. Astrotholus infernalis n. gen. n. sp.

Figures

FIGURE 2. Astrotholus infernalis n. gen. n. sp. USNM 1122403. A. Abactinal surface. B. Close view of abactinal, superomarginal and inferomarginal plates, covered by spinelets. C. Abactinal and superomarginal plates denuded. D. Oral view close view. E. Oral surface. F. Furrow and adambulacral spination.

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.