Astrotholus molginos, Mah, 2023

Mah, Christopher L., 2023, New Genera, Species, and observations on the biology of Antarctic Valvatida (Asteroidea), Zootaxa 5310 (1), pp. 1-88 : 17-19

Astrotholus molginos n. gen, n. sp.

FIGURE 4A–F

Etymology

The species epithet molginos refers to the Greek “of hide or skin” alluding to the dermis which covers the body surface of this species.

Diagnosis

Stellate body with R/r=1.2–2.0, abactinal plates imbricate, irregular on disk but showing strongly linear, transverse series interradially ( Fig. 4A, B, D ). Body surface covered by thin dermal tissue ( Fig. 4D, E ). Abactinal plates with 1–9, usually 2–4 short glassine spinelets with most arranged on the convex side of the imbricate plates ( Fig. 4D, E ), in single series interradially but in clusters elsewhere. Furrow spines 3 to 6 (at R= 2.2 cm), webbed in weakly palmate to straight series. Subambulacral spines two or three in a cluster standing apart from furrow spines, at transverse to oblique angle ( Fig. 4F ).

Comments

Astrotholus molginos n. gen. n. sp. appears to be the most morphologically dissimilar relative to the other species within Astrotholus n. gen. This is attributed to the flattened plates, as well as the dermis present on the abactinal surface and the relatively simple spination rather than the granuliform spinelets present in Astrotholus antarcticus ( Fisher, 1940) . This species shares the greatest morphological affinity with Astrotholus infernalis n. gen. n. sp.

Occurrence Scotia Sea, South Atlantic, 2886–3876 m.

Description

Body stellate, R/r=1.2–2.0, disk strongly arched and centrally rising up above surface on arms triangular, interradial arcs weakly curved ( Fig. 4A, B ). Lateral edge thin and flat. No specimens found larger than R= 2.2 cm. Body surface covered with thin dermal tissue layer ( Fig. 4A, B, D, E ).

Abactinal plates flat and round in outline, imbricate ( Fig. 4B, D ). Each plate with short glassine spinelets 1–9, mostly 2–4 located on proximal (non-imbricate) convex end of plate. Remainder of plate bare lacking accessories. Spinelets in clusters on most plates but arranged single file on interradial disk plate surfaces. Plates largest on disk and radial regions along arms, smallest distally on interradial regions on disk. Disk and radial arm plates in irregular arrangement in contrast to those interradially, which are present in ordered, transverse series from disk and radial arm plates to superomarginal plates ( Fig. 4E ). Interradial ordered plates more elongate than those on central disk region ( Fig. 4B, D ). Anus flanked by approximately four abactinal plates with spinelets directed over opening. Papulae in single pores, four to six, observed at base of arms and on disk but concealed by imbricate plates. Madreporite polygonal in shape with shallow sulci. No pedicellariae observed.

Marginal plates form scalloped lateral edge around periphery of body, with distinct spacing present between plates ( Fig. 4B, D, E ). Superomarginals present on abactinal surface, inferomarginals on actinal surface. Superomarginal plates offset, alternating in series with transverse interradial plate series. At R=1.2, approximately 60 marginal plates are present in each interradius versus 40 per interradius at R= 0.9 cm. Superomarginals quadrate to round, flattened to convex with short spinelets, 1 to 4 present on surface. Inferomarginals round, offset contact with superomarginals. Inferomarginals 1:1 with actinal plate series, which are present in distinct, ordered linear series on actinal surface ( Fig. 4F ). Terminal plates large, approximately the size of 10 adjacent marginal plates, broadly triangular.

Actinal intermediate areas forming distinct linear rows in each interradius with each actinal plate series showing direct correspondence between the inferomarginal plates to an adambulacral plate ( Fig. 4C ). Each actinal plate round, imbricate, covered by a thin dermal tissue. Each plate with spinelets, 1 to 3 with greatest number proximally.

Furrow spines webbed, 3 to 6 (at R=0.8 to 2.2) highest number proximally decreasing distally ( Fig. 4F ). Furrow spines in more palmate curve proximally becoming nearly straight midway to distally along arm. Subambulacral spines two or three in a cluster standing apart from furrow spines, at transverse to oblique angle ( Fig. 4F ). Oral plates prominent with raised central ridge, furrow spines on oral plates, 7 to 8. Fissure between oral plates well developed. Living color unknown.

Figures

FIGURE 4. Astrotholus molginos n. gen. n. sp. USNM 1659633 Holotype. A. Abactinal surface. B. Lateral view showing off plates and plate patterns. C. Actinal surface. D. Abactinal-lateral and marginal plates. E. Contact between abactinal and marginal plates showing thickened dermis over plates. F. Actinal surface showing furrow spines and plate patterns on actinal intermediate plates.