Sthenaster emmae, Mah & Nizinski & Lundsten, 2010

Mah, Christopher, Nizinski, Martha & Lundsten, Lonny, 2010, Phylogenetic revision of the Hippasterinae (Goniasteridae; Asteroidea): systematics of deep sea corallivores, including one new genus and three new species, Zoological Journal of the Linnean Society 160 (2), pp. 266-301 : 274-276

STHENASTER EMMAE SP. NOV.

FIGURE 4A–H

Occurrence: Known only from Savannah Banks and off the coast of Jacksonville, FL. 252–501 m.

Material examined: HOLOTYPE: USNM 1124468 , Savannah Banks, 31°42′N, 79°07′W, 498 m, coll. T. Casazza, JSL 4902, 26.x.2005 (1 wet spec. R = 9.6, r = 4.7). PARATYPE-USNM E15539, off coast of Jacksonville, FL, North Atlantic Ocean. 30°31′N, 80°05′W, 252 m (1 dry spec. R = 9.3, r = 4.4); PARATYPE- USNM 1124469 , Savannah Banks, 31°44′N, 79°05′W, 501 m, coll. C. Caddigan, JSL 4900, 22.x.2005 (1 dry spec. R = ~9.2, r = 4.8).

Etymology: Genus is derived from sthenos, Greek for ‘strength’ and – aster for ‘star.’ Specific epithet is named after Dr Emma Bullock in honour of her contributions to the geochemistry of meteorites and asteroids.

Description: Arms five, triangular in outline. Disk large, broad, swollen, especially in wet specimen. Body stout, thick ( Fig. 4A, B ).

Abactinal plates round to polygonal to oblong in outline with numerous interspersed secondary plates ( Fig. 4F ) embedded in a thick, pulpy tissue forming heavily thickened abactinal body wall ( Fig. 4A ). Plates with high-aspect; mound-like in shape, forming deep but open channels between plates ( Fig. 4A, E ). Abactinal plates are covered with two to ten blunt to conical spine-like granules, usually forming a periphery around plate edge with only one or two granules/ spines centrally located. Some plates bear enlarged conical, spine-like granules, surrounded by smaller blunt spinelets. Large abactinal clam-shell like pedicellariae present, each with nine to 12 interlocking teeth per valve ( Fig. 4E ). Pedicellariae located centrally on plate surface varying in size from one-third to three-quarters of plate diameter, flanked by spinelike granules. Pedicellariae occurring unevenly over abactinal surface, becoming densely concentrated in some areas but absent from others. Madreporite sunken, bordered by seven to eight abactinal plates. Papulae, small, four to six, interspersed between plates.

Marginal plates wide (W> L), 42–45 per interradius (from armtip to armtip), which become smaller and with more equivocal dimensions distally adjacent to terminal. Large spines absent from marginal plates series. Fasciolar channels present between marginal plates, relatively deep ( Fig. 4H ). Superomarginals facing laterally, correspond 1:1 to inferomarginals along most of series with one to two plates irregularly offset, possibly because of sublethal predation. Superomarginal plate surface convex, bare except for 20–35 widely spaced, sharp, conical spinelets, which are most densely concentrated ventrally on plate at contact with inferomarginal plate ( Fig. 4H ). One to two relatively small clam-shell like pedicellariae with interlocking teeth present on nearly every marginal plate but regularly present, adjacent to inferomarginal contact, irregularly present closer to contact with abactinal surface. Periphery of each plate with 15–40 small evenly spaced conical spinelets, which occur more densely at contact with inferomarginals. Inferomarginal plates with ventral facing and more densely covered by ten to 70 irregularly sized conical to blunt spinelets. Higher number of larger, conical, more pointed spinelets present closer to superomarginal contact. Higher numbers of spinelets present inter-radially decreasing distally corresponding with smaller inferomarginal plate size. Pedicellariae, one to four, typically two, identical to the type on superomarginals present on inferomarginals facing ventrally. Terminal plate round, bulbous.

Actinal intermediate plates, similar in size, shape to abactinal plates with well-developed fasciolar channels running between plates ( Fig. 4C, D ). Actinal plate series adjacent to adambulacral plate series with large pedicellariae nearly equal to size of plate on which it sits ( Fig. 4C, D ), teeth poorly developed to absent relative to those on abactinal plates. Pedicellariae on actinal series adjacent to adambulacral plates occur with less frequency distally along the arm with some smaller actinal plates adjacent to armtip with pedicellariae absent, bearing only three to six spinelets. Actinal pedicellariae occur most heavily adjacent to mouth, becoming less common to absent adjacent to inferomarginal plate contact. Pedicellariae on each actinal plate surrounded by 20–35 sharp spinelets, some round, some triagonal to polygonal in cross-section ( Fig. 4C, D ). Actinal plates adjacent to inferomarginal plate series covered with four to 30 sharp, irregularly sized, conical granular spines. Some with polygonal to triangular in crosssection. Oral cavity sunken ( Fig. 4B, C ).

Adambulacral furrow spines blunt tipped, three to four per plate, triangular to oblong ovate in crosssection in weakly convex series ( Fig. 4G ). Distinct grooves between adambulacral plates. Central spines longest and thickest with spines shortest on ends. Subambulacral spines three in two series. Subambulacral spine series adjacent to furrow spines somewhat shorter than furrow spines but comparable in thickness, round to oval in crosssection ( Fig. 4G ). Subambulacral spine series farthest away from furrow spines shortest, with central spines only slightly less thick than furrow spines with smallest spines located on ends of second subambulacral series. Distinct fasciolar channel separates adambulacral plates from actinal intermediate plates.

Oral plates with four to six furrow spines. Oral plate surface with three to four spines per plate (six to eight total on paired oral plates) with one to three spines projecting into oral opening ( Fig. 4C ). Spines triangular to flattened triangular in cross-section, most are comparable in length to furrow spines but sometimes with one or two that are similar to granular spines.

Colour in life is orange.

Habitat description: The holotype was collected on hard substrata covered by the gorgonian Eunicella modesta ( Verrill, 1883) . Other unidentified gorgonians, the scleractinian Lophelia pertusa , sponges, and coral rubble were observed at the collection site. The paratype was collected from Savannah Banks on hard substrata where various gorgonians, sponges, scleractinian corals, and coral rubble were also present.

Figures

Figure 4. Sthenaster emmae gen. et sp. nov. USNM 1124468. A, abactinal surface; B, actinal surface; C, oral region; D, actinal-inferomarginal contact; E, close-up of abactinal surface showing pedicellariae; F, close-up of abactinal plates on armtip; G, adambulacral furrow spines; H, marginal plates – lateral facing of superomarginal plates. Scale bars: A, B = 10 mm; C–H = 5 mm.