Eratosaster jenae

Mah, Christopher L., 2011, Taxonomy of high-latitude Goniasteridae (Subantarctic & Antarctic): one new genus, and three new species with an overview and key to taxa, Zootaxa 2759, pp. 1-48 : 24-25

Eratosaster jenae nov. sp.

( Figure 10 A–D)

Diagnosis. Body strongly stellate. Abactinal plates strongly convex. Abactinal, marginal, and actinal plates bare and smooth with only peripheral granulation. Abactinal, marginal, and actinal plates with large conical spines. Furrow spines elongate, forming distinct spiny fringe on tube foot furrow. Subambulacral spine also elongate similar in size to furrow spines.

Etymology. The genus is derived from the Greek Eratos for “lovely” and – aster for “star”. The species epithet, “ jenae ” is named for Dr. Jen Hammock, administrator of the US Antarctic Research Program, which has supported Antarctic biodiversity research and collections.

Distribution. South Atlantic ( Scotia Sea ), Burdwood Bank. 339–1886 m.

Material examined. HOLOTYPE: USNM 1149358 Burdwood Bank 54°42’S, 56° 36’ W, 339– 357 m. Coll. R/V Eltanin st. 1593, 14 March 1966 (1 dry spec. R=4.2, r=1.3).

PARATYPES: USNM 1149359, Scotia Sea , SE of Burdwood Bank, off Falkland Islands 54°0’0”S, 55°53”W, 1879–1886 m. Coll. R/V Eltanin st. 377, 21 December 1962 (1 dry spec., R=4.0, r=1.4). USNM 1149360. Burdwood Bank 54°42’S, 56° 36’ W, 339– 357 m. Coll. R/V Eltanin st. 1593, 14 March 1966. (1 dry spec. R=3.8, r=1.3).

Description. Body stellate. Arms elongate, triangular. Interbrachial arcs weakly rounded ( Fig. 10 A–B). Disk from (USNM 114358, 114360) is more convex with armtips curled upwards on Burdwood Bank specimens compared to the Scotia Sea specimen (USNM 1149359), which is more flattened.

Abactinal plate surface convex, smooth, devoid of accessories (e.g., granules, etc.). Convexity strongest on disk with plates becoming more flattened distally along arm. Abactinal plate in dorsal outline, perfectly circular to oval, often irregular in shape with rounded edges. Fasciolar grooves weakly present. Largest and roundest proximally becoming smaller and more irregular distally towards contact with superomarginal plate series. Abactinal plates present along arm, sometimes to terminal plate but sometimes present only proximally on arm. Distribution and shape of abactinal plates on disk varies even on arms on one individual (e.g., paratype USNM 1149360). Presence of abactinal plate to armtip varies among individuals and is present in holotype but not in paratype from Scotia Sea (USNM 119359), which shows superomarginal plates abutting over midline distally on arm ( Fig. 10 D). Disk plates with spines. Spines thick and stout, conical with blunt to pointed tips. When present, spines present centrally on each plate, located primarily on disk but holotype has spines on series extending out along proximal portion of arm ( Fig. 10 A, B). Papulae present between plates in radial regions on disk, but absent from distal arm regions and interradial regions, especially at contact with superomarginal border. Accessory granules round to teardrop to triangular in shape, present between disk plates but becoming less abundant distally along arms especially on specimens where abactinal plates do not form series directly to armtip.

Superomarginals 25–30 per interradius (from armtip to armtip). Inferomarginals 28–30 per interradius (from armtip to armtip). Superomarginals and inferomarginals are larger interradially becoming smaller distally, becoming closer in size (more 1:1) interradially, and becoming more offset distally. A zigzag contact between superomarginals and inferomarginals is more clearly present distally, where the plates are more offset. Both marginal plate series are convex. Plates in both series with a single stout, conical spine similar to the ones present on the abactinal plate. Other then the large single spine, marginal plate surface is smooth with no other accessories present. Some plates have a second, smaller spine present. Large spines on marginal plates in series facing laterally forming a distinct fringe around the marginal plate edge. Spines are more dorsolaterally directed interadally, becoming more directly lateral-facing on distal part of arm. Dorsal-facing marginal plates distally are more flattened relative to those interadially which are more rounded. Small granules, ~50–60 (~13–15 per side), each round to elongate to teardrop shaped, present as periphery around each marginal plate, although granules are absent (likely due to abrasion on many plates).

Actinal surface is made up of two chevrons of plates, including an irregular array of these plates adjacent to the contact with the inferomarginal plate series ( Fig. 10 C). The complete chevron is adjacent to the adambulacral plate series and is limited to the proximal region of the arm. Actinal plates absent distally along the arm. Plates are irregularly round, forming trapezoids, ovals, or other irregular shapes. Most plate surfaces are bare but several of the smaller plates adjacent to the inferomarginal plate series each bear a large, prominent conical spine similar to the spines present on the abactinal and marginal plates. Actinal plates, each surrounded by peripheral granules, 15–25 in number, round to teardrop in shape, and mildly convex to flat in profile ( Fig. 10 C). Some are convex with a weak point.

Furrow spines generally two proximally (distally or exceptionally three), but spine size is variable ( Fig. 10 C). Proximal furrow spines both blunt, elongate, round in cross-section at base, becoming more flattened at tip. More distal furrow spines, starting around the fifth or sixth adambulacral plate, with disproportionately smaller distal spine versus proximally, much larger spine. Larger spine is easily two to three times the length and width of the smaller spine. A third furrow spine is present distally near the armtip on adambulacral plates in the two Burdwood Bank specimens but occurs on nearly every proximal adambulacral on the Scotia Sea specimen. Furrow spines, three to four, on each oral plate. Each subambulacral spine is large, prominent, equal to if not larger then largest of the furrow spines. Pointed to blunt-rounded granules, four to six, present behind subambulacral adjacent to actinal plate series. Large paddle-like pedicellariae present on one adambulacral plate out of every 10, usually on surface adjacent to actinal plate series. Infrequently observed on three specimens examined.

Comparisons with other taxa. Eratosaster closely resembles the genus Calliaster but differs in several different respects. Calliaster , based on morphological definitions by Mah (2005) and H.E.S. Clark (2001) is supported by several characteristics, including smooth, bare, swollen marginal plates with prominent conical to blunt spines, abactinal plates with granular accessories forming a discrete periphery, large, conical subambulacral spines in a transverse series to the tube foot furrow, and furrow spines usually very numerous (> 10 in most species and> 15 in several). Eratosaster has only a single enlarged, conical subambulacral spine on each adambulacral plate that precludes having them in a transverse series. Eratosaster also only has two to three furrow large, thickened spines which differs from nearly all Calliaster sp. except for Calliaster baccatus which has three. The numerous peripheral granules that occur between marginal plates in nearly all Calliaster species are also poorly expressed between the marginal plates on Eratosaster . However, Eratosaster does have bare, swollen abactinal and marginal plates along with large, blunt conical spines centrally located on several of these plates. Calliaster and related taxa, including Astrothauma , Milteliphaster and Mabahissaster are members of a complicated species complex (Aziz and Jangoux 1982). Unpublished diversity of species in this group is much greater then what is observed in published accounts (Mah, unpublished data) and this represents one of the first accounts of this group from the Atlantic.

Eratosaster appears intermediate between Calliaster and the Antarctic goniasterid Chitonaster . Chitonaster has enlarged furrow and subambulacrals similar to those in Eratosaster but abactinal and marginal plate morphology in Chitonaster differs substantially from Eratosaster . Some morphology does suggest relationship between Calliaster and Chitonaster , which suggests Eratosaster may be an important potential sister taxon for outgroup consideration in phylogenetic studies.

Figures

FIGURE 10. Eratosaster jennae n. sp. Holotype. USNM 1149358 A. Abactinal surface. B. Abactinal-lateral surface showing spines and superomarginal series. C. Actinal surface and oral region. D. Armtip showing superomarginals abutted along midline. Scale Bar = 0.5 cm.