Astrotholus phasma, Mah, 2023

Mah, Christopher L., 2023, New Genera, Species, and observations on the biology of Antarctic Valvatida (Asteroidea), Zootaxa 5310 (1), pp. 1-88 : 20-22

Astrotholus phasma n. gen. n. sp.

FIGURE 5A–F

Etymology

The species epithet phasma is derived from the Greek for ghost or spirit, alluding to the strongly arched ghostlike shape of this species.

Diagnosis

Abactinal plates flat to mound-like surface covered by simple spinelets, 4–10 ( Fig. 5B, C ). Transverse interradial plates similar in size to radial abactinal plates ( Fig. 5C ). Superomarginal plates approximately twice the size of the inferomarginal plates ( Fig. 5E ). Furrow spines webbed, pointed, 2 to 7 in palmate formation. Subambulacral spines with identical spination, 3 to 6 in a straight to weakly palmate comb, arranged in oblique to transverse position relative and set off from the furrow spine by a distinct space ( Fig. 5D, F ). Largest size among type series R =2.5.

Comments

This species represents the only known occurrence of the genus in the South Atlantic, and outside of the Southern Ocean region.

As indicated in the description, this species also displays the arched body form and what appears to be eggs present around the oral region ( Fig. 5F inset). If ultimately confirmed as a brooding species, it would join Kampylaster incurvatus as the second high-latitude asterinid to display this behavior.

Occurrence South Atlantic , Burdwood Bank , Drake Passage and Ross Sea 339–528 m.

Description

Body stellate (R/r=1.2–2.0), strongly arched ( Fig. 5A, B, C ), disk thickened, actinal surface convex, arms triangular. Interradial arcs acute.

Abactinal plates imbricate, polylobate, larger plates on disk, arm plates smaller, most <50% of the size, some close to 25% of the size of those on the disk ( Fig. 5A, B, C ). Plates mostly flat, larger plates weakly mound-like. Abactinal plates covered by simple spinelets, 4–10, widely spaced, arranged in single series or only along edge of each plate with central region devoid of spination ( Fig. 5B, C, E ). Shallow furrows present between plates. Interradial plates in distinct transverse rows between the radial abactinal arm plates and the superomarginal plates. Transverse plates are similar in size to those on the radial regions. Papulae 10–15 per radius, in single or double series along radius of arm, emerging between lobate edges on exposed plates or between plates on disk.

Marginal plates 32–40 (16–20 per arm) per interradius (arm tip to arm tip) at R=0.9 to R=1.1. Superomarginal plates approximately twice the size of the inferomarginal plates ( Fig. 5E ). Both marginal plate series imbricate, superomarginals quadrate with rounded edges, inferomarginals ovate, at oblique angle to superomarginals. Superomarginals with spinelets, 3 to 6, identical to those on the abactinal plates, inferomarginals with 4 to 10 spinelets. Superomarginal and inferomarginal imbrication arrangement presents a crenulate outline around the periphery of the body. Terminal plate quadrate (trapezoidal) approximately the size of two adjacent superomarginal plates with no spines or granules.

Actinal plate region with imbricate, transverse series, plates elongate, forming direct association between inferomarginals and adambulacral plates ( Fig. 5D ). Each plate with a comb of short spinelets 3 to 6, mostly 3 to 4 on each plate. These actinal spine combs are even but closely spaced presenting a very spiny actinal surface.

Furrow spines webbed, pointed, 2–7 in palmate formation ( Fig. 5D ). Subambulacral spines 3–6 with identical spine length in a straight to weakly palmate comb, arranged in oblique to transverse position relative and set off from the furrow spine by a distinct space.

Brooding Observation?

One of the paratypes showing what appear to be 4 round, yolky eggs around the mouth ( USNM 1662096 ), one tiny specimen which was found in loose relationship with the mouth of the specimen ( Fig. 5F and inset). It is unclear if this was a brooded juvenile.

Material Examined

Holotype: USNM 1662096 , Burdwood Bank, Scotia Sea , South Atlantic Ocean , −56.108, −66.408, 384–494 m. Coll. R/V Eltanin, 18 Sept. 1963. 1 dry spec. R=1.0 r=0.6 (with brooded eggs/embryos).

Paratypes: USNM 1659628 , Burdwood Bank, Scotia Sea , South Atlantic Ocean . −54.708, −56.633, 339–357 m. Coll. R/V Eltanin, 14 March 1966. 1 dry spec. R=1.0 r=0.6.

USNM 1659629 , Drake Passage , Tierra Del Fuego, Argentina. −56.108, −66.408, 384–494 m. Coll. R/V Eltanin, 18 Sept. 1963. 5 dry specs. R=0.8 r=0.4, R=1.1 r=0.9, R=1.1 r=0.7, R=1.1 r=0.8, R=0.8 r=0.5, R=1.3 r=0.9.

USNM 1660654 , Cape Horn, Tierra Del Fuego , Drake Passage , South Atlantic . −56.108, −66.408, 384–494 m. Coll. R/V Eltanin, 18 Sept. 1963. 1 dry spec. R=0.2 r=0.1.

USNM 1662097 , Victoria Land, Ross Sea , −72.008, −172.508, 523–528 m. Coll. R/V Eltanin, 10 Jan. 1968. 6 dry specs. R=0.4 r=0.3, R=0.4 r=0.3, R=0.4 r=0.3, R=0.5 r=0.4, R=0.4 r=0.3, R=0.35 r=0.25.

Figures

FIGURE 5. Astrotholus phasma n. sp. USNM 1662096 Holotype. A. Abactinal surface. B. Side view showing surface texture, plates and other details. C. Abactinal plates cleared showing plate shapes, transition with spined plates. D. Actinal view, actinal plates cleaned, furrow and adjacent spination. E. Close up lateral view of cleaned abactinal and marginal plates near armtip. F. Further view of actinal surface, mouth and oral region. Inset: brooded eggs/embryos (each about 1.0 mm across).