Lophaster abbreviatus Koehler, 1907

Mah, Christopher L., 2023, New Genera, Species, and observations on the biology of Antarctic Valvatida (Asteroidea), Zootaxa 5310 (1), pp. 1-88 : 51-54

Lophaster abbreviatus Koehler, 1907

FIGURE 16 A–E

Lophaster abbreviatus Koehler, 1907: 144 ; 1908: 557; A.M. Clark 1962: 50.

Diagnosis

A stellate species (R/r=2.3–2.4) with strongly arched disk, short triangular arms, interradial arcs weakly curved to straight ( Fig. 16A ). Abactinal paxillar shaft very short, bearing 2 to 4 elongate hyaline spines, weakly serrated widely spaced over the abactinal surface ( Fig. 16B ). Marginal paxillae approximately 22–24 per interradius (11–12 per arm), widely spaced, each shaft round in cross-section bearing 3–6, mostly five, fine hyaline spines ( Fig. 16C ). Sequential adambulacral plates separated from one another by opaque tissue. Furrow spines 3 on first adambulacral plate, then mostly 2, and a single spine on distalmost adambulacral plates. Subambulacral spines 3, then single along arm ( Fig. 16D, E ). Oral plates with raised, distinct ridges, furrow spines on oral plates 7 to 9, identical to furrow spines on adambulacral plates. No spines on oral plate surface.

Comments

This represents the first account of this species since its description by Koehler (1908). Lophaster abbreviatus Koehler, 1908 was argued as a synonym of Lophaster stellans by A.M. Clark (1962). Specimens examined herein, which included specimens collected from the South Orkney Islands near the type locality (specimens from −59.975, −49.233, type specimen from −62.167, −41.333) support L. abbreviatus as a distinct species, varying only in minor respects from Koehler’s (1908) description.

Examined specimens are all larger than the holotype (R= 1.1 cm) but show a similar overall R/r=2.3–2.4 versus the holotype R/r=2.2 as well as a thick disk and short, stocky triangular arms. Specimens herein possess 3 to 8, mostly 4 elongate abactinal hyaline spines with weak serrations which are longer than the short, stocky peduncle of each paxillae. There are 11 to 12 marginal paxillae per arm, versus the 10 on the holotype. The fewer paxillae could be explained by the smaller size of the holotype (R= 1.1 cm). Specimens have three furrow spines, decreasing to two distally, which is identical to the adambulacral spination on the holotype. Spines on the oral plate varies among specimens herein, ranging from 6 to 8 which is again consistent with the 7 or 8 described by Koehler (1908).

Lophaster abbreviatus has been mostly closely compared with L. stellans but differs significantly based on a larger disk and shorter arms (R/r=2.2–2.4), having elongate single point spines with serrate edges that extend past the squat pedunculate base versus short paxillar spinelets having flanged, multi-pointed tips, and a pedunclelike paxillae versus a paxillae with an elongate shaft. Lophaster abbreviatus also displays 3 then 2 furrow spines (proximal then distal) versus 4 then 3 in L. stellans .

The squat pedunculate abactinal plate base with elongate spines ( Fig. 16A, B ) in L. abbreviatus distinguishes this species from all the other high-latitude Lophaster species.

The very deep depth range of this species (2886–3944 m) further separates this species from Lophaster stellans , which has a largely shallow range (18–463 m) that does not show overlapping range with Lophaster abbreviatus . If Lophaster abbreviatus is removed from the potential synonymy of Lophaster stellans , it is the deepest-known of the high-latitude Lophaster species.

Occurrence

Georgia and South Orkney Islands, Scotia Sea, 2886–3944 m.

Description

Body thick, stellate (R/r=2.3–2.4), arms broad based, triangular, interradial arcs weakly curved to acute. Abactinal surface, strongly convex ( Fig. 16A ).

Abactinal plates forming widely meshed reticulate network, skin present between reticulated plates. Paxillae with quadrate bases but also part of irregular net-like patterns over body surface. Individual plates cylindrical, short, overlapping. Smaller, individual irregular plates present distally on arm. Individual paxillar shaft short, each bearing mostly 2 to 4, spines radiating out from paxillar base ( Fig. 16B ), each spinelet serrated with hyaline tip. Surface covered by thin dermis. Paxillar plates occurring more closely together along arm tips than on disk. Madreporite polygonal to oval, raised above surface with well-developed sulci. Paired “fold” of abactinal plates present in each interradius on disk.

Marginal paxillae 22 per interradius (approximately 11 per arm), superomarginal and inferomarginal plates approximately similar in size ( Fig. 16C ), widely spaced from one another serially along arm ( Fig. 16E ) as well as laterally with distinct gap separating the superomarginal from the inferomarginal. Each plate, round in cross-section, each with 3 to 6, mostly 5, spines with hyaline tips. Marginal plates appear to be embedded within an opaque dermis present between plates along lateral and actinal areas. Inferomarginal series encroaching onto actinal intermediate regions forming rounded actinolateral surface. Terminal plates large, approximately the same size as three adjacent superomarginals, with distinct notch present centrally.

Actinal intermediate region with one or two irregular reticulated plates, bearing two spines, but otherwise covered by an opaque dermis ( Fig. 16D ).

Adambulacral plates separated from one another by opaque tissue. Furrow spines 3 on first adambulacral plate, then mostly 2, a single spine on distalmost adambulacral plates. Each spine slender and elongate, weakly webbed at base. Subambulacral spines 3, then single along arm. Oral plates with raised, distinct ridges, furrow spines on oral plates 7 to 9, these identical to furrow spines on adambulacral plates ( Fig. 16D, E ). No spines on oral plate surface.

Material Examined

USNM 1418038, Georgia Island, Scotia Sea, South Atlantic Ocean, −55.092, −39.842, 2886–3040 m. Coll. R/V Eltanin, USAP, 8 Feb. 1966. 28 dry specs. R=1.3 r=0.5, R=1.3 r=0.6, R=1.3 r=0.6, R=1.8 r=0.8, R=1.3 r=0.5, R=1.7 r=0.7, R=1.7 r=0.6, R=0.8 r=0.3, R=1.3 r=0.5, R=1.5 r=0.5, R=1.7 r=0.7, R=1.4 r=0.6, R=1.6 r=0.6, R=1.1 r=0.4, R=2.0 r=1.3, R=1.3 r=0.6, R=1.3 r=0.6, R=1.3 r=0.6, R=1.7 r=0.7, R=1.5 r=0.7, R=1.0 r=0.5, R=1.5 r=0.6, R=1.0 r=0.5, R=1.1 r=0.5, R=1.1 r=0.5, R=1.1 r=0.5, R=1.3 r=0.8, R=1.0 r=0.3.

USNM 1468790, Scotia Sea, South Atlantic Ocean, −57.867, −56.85, 3788–3944 m. Coll. R/V Eltanin, USAP, 24 Jan. 1966. 1 dry spec. R=2.8 r=0.9.

USNM 1573488, South Georgia Island, Scotia Sea, South Atlantic, 3623–3714 m. Coll. R/V Eltanin, USAP, 12 Feb. 1963. 1 dry spec. R=1.8 r=0.7 (arm tips broken)

USNM 1573678, Scotia Sea, South Atlantic Ocean, −59.025,−51.875, 3010–3510 m. Coll. R/V Eltanin, USAP, 26 Jan. 1966. 12 dry specs. R=1.8 r=1.4, R=1.3 r=0.5, R=2.1 r=0.9, R=1.8 r=0.7, R=1.4 r=0.6, R=1.4 r=0.6, R=1.5 r=0.6, R=1.1 r=0.5, R=2.4 r=1.3, R=2.2 r=1.1, R=2.1 r=1.2.

USNM 1573489, SE of South Orkney Islands, Scotia Sea, Southern Ocean, −62.15, −40.642, 3250–3285 m. Coll. R/V Eltanin USAP, 24 March 1964. 2 dry specs. R=1.5 r=0.7, R=1.5 r=0.6,

USNM 1660590, South Orkney Islands, Scotia Sea, −59.975, −49.233, 3819–3876 m. Coll. R/V Eltanin, 7 March 1963. 1 dry spec. R=2.2 r=0.9.

USNM 1660600, South Orkney Islands, Scotia Sea, −59.975, −49.233, 3819–3876 m. Coll. R/V Eltanin, 7 March 1963. 1 dry spec. R=1.8 r=1.0.

USNM 1675791, NW of South Orkney Islands, Scotia Sea, Southern Ocean, −58.975, −49.142, 3867 m. Coll. R/V Eltanin, USAP, 8 March 1963. 1 dry spec. R=2.0 r=1.0.

Figures

FIGURE 16. Lophaster abbreviatus USNM 1660590. A. Abactinal surface. B. Closeup showing paxillae with spinelets. C. Actinal surface. D. Closeup of oral and furrow spine region. E. Closeup of furrow spine and marginal paxillae.