Goniodiscaster aegis, Mah, 2018

Mah, Christopher L., 2018, New genera, species and occurrence records of Goniasteridae (Asteroidea; Echinodermata) from the Indian Ocean, Zootaxa 4539 (1), pp. 1-116 : 39-44

Goniodiscaster aegis n. sp.

Figure 15 A–F

Etymology. The species name aegis is taken from the Greek for “shield” alluding to the flattened, shield-like form of the granules on the abactinal and especially on the marginal plates.

Diagnosis. Abactinal, marginal and actinal surface covered by round to scalar granules, widely spaced across the abactinal, marginal and actinal surfaces. Furrow spines five to seven, and two distinct rows of subambulacral spines, the first adjacent series with two or three then the third row with two to five ( Fig. 15E ).

Comments. Goniodiscaster aegis n. sp. is most immediately compared with Goniodiscaster forficulatus ( Perrier 1875) which is similar in arm and body shape. Goniodiscaster aegis n. sp. is distinguished based on the presence of flattened, and convex but scalar granules covering the abactinal, marginal and actinal plate surface, which are contrasted to the spiny granules present on the abactinal, marginal and actinal plate surface of Goniodiscaster forficulatus . Goniodiscaster aegis n. sp. is also differentiated based on the fewer furrow spines (five to seven) versus the eight to 10 furrow spines in Goniodiscaster forficulatus . Goniodiscaster aegis n. sp. also lacks pedicellariae (present in Goniodiscaster forficulatus ) and possesses fewer subambulacral spines (2 or 3 and 2 to 5 in first and second row) relative to Goniodiscaster forficulatus (3 to 5 and 3 or 4 in first and second row).

Occurrence. Off Northeast coast, Somalia, 27– 31 m.

Description. Body stout, stellate (R/r=2.47), arms triangular, elongate, arm tips pointed, upturned. Interradial arcs broadly curved ( Fig. 15A ).

Abactinal surface composed of abutted, convex plates ( Fig. 15B ). Carinal plates enlarged, broad approximately twice the size of adradial abactinal plates proximally and forming a distinct, more elongate adjacent to arm tip ( Fig. 15A ). Other abactinal plates distinctly convex, but smaller, more irregular in shape. Each interradius with three paired plates present in each interradius creating a deep contact or fold between them which directly corresponds to paired interradial superomarginal plates ( Fig. 15B ). Abactinal plates continue along arm to penultimate superomarginal plates adjacent to arm tip with plates narrowing along arm to three then a single row of plates distally adjacent to terminus. Surface covered by a dense, granular tegument composed of coarse, polygonal granules, continuous and extending from abactinal to marginal plate surface. Granules larger on central plate surface approximately 3 granules counted along a 1.0 mm line versus smaller granules between the abactinal plate convexities (approximately 4 granules along a 1.0 mm line). Where granules have been removed, plates show small but coarse pitting in the surface. Papulae present, three to five per region, in concavities between more strongly convex plates. Papulae most abundant along radial regions, absent interradially and around anus. Some papular clusters present right at contact between abactinal surface and superomarginal plates. Anal opening with approximately four to six flattened, blade-shaped spines covering anus. No tubercles or any other prominent accessories on disk or arm surface. Madreporite polygonal to round with four to size angles, flanked by approximately six abactinal plates. No pedicellariae observed on abactinal surface.

Marginal plates 30–32 per interradius, arm tip to arm tip (i.e., 15–16 per side) in both superomarginal and inferomarginal series. Superomarginal plates wide, surface strongly arched with rounded edges becoming more quadrate distally with length and width becoming more similar ( Fig. 15C ). Tubercles, small, pointed present on distalmost two to three penultimate superomarginal plates on three arms but absent on a fourth (fifth arm tip broken). Distalmost superomarginal plates abutted over midline along mid-radius. Both superomarginals and inferomarginals thickest and with most pronounced thickness interradially, displaying raised lateral surface. Marginal plate surface, as with abactinal surface, covered by large, flattened, widely spaced polygonal coarse granules, approximately 200–500, which can be as large as 1.0 mm wide on the central top surface of the superomarginal plates but are smaller, approximately two to three per 1.0 mm on the elsewhere on the surface of the plate. Granules smaller at lateral contact between superomarginal and inferomarginal plates. Inferomarginal surfaces covered by uniform smaller, coarse, scalar granules, approximately 200–500, widely spaced with two to three granules present along a 1.0 mm line, evenly spaced on the plate surface. Distalmost three to four inferomarginal plates also with short spine-like tubercle or spinelet, but presence is inconsistent on arms examined. Granular cover is continuous with no distinction between central and peripheral granules other than the difference in size (smaller on peripheral areas, larger centrally). Small, crystalline granules are present under granular integument. Terminal plate diamond shaped, approximately twice the size of adjacent penultimate superomarginal plates. No pedicellariae observed on marginal plate surface.

Actinal surface composed of three full series, in chevron formation limited to base of arm, with no actinal plates extending beyond fifth inferomarginal from interradius (i.e. basal 1/3 of arm) ( Fig. 15D ). Two to four plates, irregularly arranged within chevron adjacent to inferomarginal contact. Actinal plates strongly convex, round to irregularly polygonal in shape with distinct open fasciolar grooves between them. Granules absent from grooves. Large, coarse, widely spaced, round to polygonal granules, 10 to 50 present on each actinal plate surface. Granules not arranged into discrete central and peripheral series.

Furrow spines five to seven, blunt tipped, quadrate in cross-section in widely splayed, palmate formation with smaller spines on sides, longest spines medially ( Fig. 15E ). Furrow spines on some plates extended and intercalated between adjacent subambulacral spines. Two subambulacral spine series adjacent to furrow spines, the adjacent series composed of two or three broad, thick spines, approximately 1.5 to twice the width of the furrow spines but approximately the same length. Third subambulacral spine series composed of two to five, but primarily three, (a minority with a smaller fourth spine) blunt spines, approximately 30% of the height of the taller second subambulacral spine series. Oral plate with furrow spines, ten, with blunt tips. Adjacent subambulacrals six, blunt, thick. Each oral plate with a large, thick, pointed tip directed into mouth (two on each interradius). Second subambulacral spine series on oral plate, four, short, triangular in cross-section. Oral plate surface with six to eight irregularly aligned, angular granules on either side of the oral plate sulcus. Remainder of oral plate surface with two to four pointed, angular spines widely spaced on otherwise clear oral plate surface. Pedicellariae absent from adambulacral plates.

Material Examined. Holotype. USNM E51097 Off Northeast coast, Somalia, Indian Ocean. 11°14’N 51°08’E, 27–31 m. Coll. R / V Anton Bruun, IIOE, 1 wet spec. R=4.7 r=1.9.

Figures

FIGURE 15. Goniodiscaster aegis n. sp. Holotype, USNM E51097. R=4.7, r=1.9 cm. A. Abactinal surface. Scale bar=1.0 cm. B. Closeup of abactinal surface with white box around interradial paired plates and “fold”. Scale bar=0.3 cm. C. Interradius showing superomarginal and inferomarginal plates.Scale bar=0.5 cm. D. Actinal surface. Scale bar=1.0 cm. E. Closeup of furrow and adambulacral spines. Scale bar =0.3 cm.