Mediaster roanae, 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 : 59-60

Mediaster roanae n. sp.

Figure 22 A–E

Etymology. This species is named for Dr. Jeanette Roan, a professor at the California College of the Arts in honor of her contributions to Asian-American literature.

Diagnosis. Body size strongly stellate (R/r=3.0 to 3.6) ( Fig. 22A ). Abactinal plates with granular cover composed of pointed, cylindrical-shaped granules, seven to 60. Coarse, larger granules present centrally, numbering 15–25 ( Fig. 22B ). Superomarginals ( Fig. 22C ) with lateral facing interradially, becoming more upwards facing distally. Marginal plates 74–82 per interradius (37–41 per side), granules on marginal plates pointed. Tonglike pedicellariae not observed on abactinal surface but present on marginal and actinal surfaces. Furrow spines seven to 12, 10–12 proximally ( Fig. 22E ).

Comments. This species closely resembles and is likely related to Mediaster murrayi Macan 1938 . Both species have tabulate abactinal plates which have coarse, widely spaced central granules seated on wide, polygonal carinal plates. Mediaster murrayi , at R=3.0– 4.7 cm, display 6 to 12 granules whereas M. roanae n. sp. at R= 9.1 cm, display 4 to 30. There is also direct continuity between the actinal and marginal fasciolar grooves at the actinal/ inferomarginal contact. Furrow spine and subambulacral spine number in M. murrayi is seven to nine and three relative to seven to 12 and two to six in M. roanae n. sp. Although the spine numbers overlap, they do show distinct count differences proximally (10–11 in M. roanae vs. six to seven in M. murrayi ). This variation might be explained by the much larger specimens of M. roanae (R=8.1 to 9.1) versus M. murrayi (R=3.0 to 4.7).

Mediaster roanae n. sp. is distinguished by the presence of pointed granules on the marginal plate surface which is contrasted to the hemispherical granules observed on M. murrayi Macan 1938 . Mediaster roanae also possesses 74–82 marginal plates per interradius (37–41 per side) versus M. murrayi which has 42–48 (21–24 per side) marginals per interradius and is more stellate with an R/r=3.0–3.6 versus R/r= 2.4–2.8 in M. murrayi . Pedicellariae are absent from the abactinal surface of M. roanae n. sp. but are present on M. murrayi . Pedicellariae were observed on the actinal surface of M. roanae n. sp. but were more triangular in shape versus those on M. murrayi which were more tong-like in outline.

Occurrence. Madagascar, 379–416 m.

Description. Body strongly stellate (R/r=3.0–3.6) arms triangular, elongate, tapering along distalmost tips. Interradial arcs broadly curved to straight ( Fig. 22A ). Abactinal surface inflated.

Abactinal plates polygonal in outline ( Fig. 22B ), especially on radial regions, becoming more round to irregularly shaped interradially. Fasciolar grooves present, most strongly developed on disk along radial regions on disk with plates flattening out distally along arms, grooves disappearing near arm tips. Abactinal plates with granular cover composed of pointed, cylindrical-shaped granules, seven to 60 ( Fig. 22B ). Plate periphery with four to 30 round, coarse, widely spaced granules, Coarse, larger granules present centrally, numbering 15–25. Carinal plates wider, displaying approximately 50 peripheral granules, four to 20 centrally. Interradial abactinal granules much more homogeneous in appearance and much more abundant, covering plates and obscuring boundaries between them and the superomarginal plates. Abactinal plate bases with radiating ossicles from radial central plate region but absent interradially. Papulae six per plate, present on each plate angle. Fasciolar channels, approximately five to seven, from interradial regions extending from abactinal surface forming direct correspondence with fascioles present along the marginal pate series. Madreporite large on observed individuals (diameter=6.0 mm) flanked by eight abactinal plates. No pedicellariae observed.

Superomarginal plates 74–82, inferomarginal plates approximately 78–90 with slight offset between superomarginal and inferomarginal plates resulting in zig-zag contact between the marginal plate series. Marginal plate quadrate in outline ( Fig. 22C ) with interradial plates displaying lateral facing but becoming more abactinalfacing near arm-tip. Inferomarginals mostly actinal surface facing. Both superomarginals and inferomarginals especially wide interradially but irregular throughout series, with some plates ranging from narrow to wide along series. Superomarginal plate series covered by 50–80, mostly 30–60 widely spaced, pointed granules similar in size, gauge as those on interradial abactinal regions. Inferomarginals covered by identical types of spines, 20–80, mostly 30–65, widely spaced. Tong-shaped pedicellariae, with elongate, slender valves approximately 1.0 mm long present on a minority of plates, approximately 1 of every 20. Fasciolar grooves along inferomarginal plates contiguous with those formed along actinal surface.

Actinal surface extensive, four to five full series in irregular chevron series with individual plates ranging from quadrate to irregularly polygonal in shape ( Fig. 22D ). Irregular plates distally adjacent to inferomarginals but regular fasciolar channels present, arranged transversely from inferomarginals to the chevron arranged series. Fasciolar grooves shallow. Actinal plate surfaces covered by widely spaced, pointed granules, eight to 30, mostly 15–25, round to triangular in cross-section. Actinal plates proximally with larger central pointed granules. Some individuals display higher abundance of granules obscuring boundaries between actinal plates. Actinal series adjacent to adambulacral plates with one pedicellaria on each plate, tong-like, about 2.0 mm long present on disk and proximally along arms.

Furrow spines, seven to 12, mostly 10 to 12, increasingly distally. Spines quadrate in cross-section, spines in straight series. Subambulacral spines, two to six, mostly three to five immediately behind furrow spines, set off from by a discrete space ( Fig. 22E ). This subambulacral series with two or three large, thick central spines with one or both distalmost spines <25% of the height of the central spines ( Fig. 22E ). These central three subambulacral spines each twice as thick as furrow spines, quadrate in cross-section, spines blunt or pointed, approximately 25% longer than furrow spines. Remaining adambulacral plate surface with low pointed spiny, widely-spaced granules, four to six. Oral plate furrow spines, 12–15, blunt, flattened with one blunt cylindrical tip pointed into mouth on each plate (two per interradius). Four distinct subambulacrals, twice as thick and approximately 25% longer. present behind furrow spines set off by discrete space. Oral plate sulcus set back from plate apex, three or four low granular spines present on either side.

Color in life was a bright orange with a light yellow to white oral surface.

Material Examined. Holotype. IE-2013-17326 Madagascar, 14°29’S 47°26’E, 379– 332 m. Coll. Bouchet and Kantor, July 14, 2009 aboard N/ O Miriky CP 3289. 1 wet spec.R=9.1, r=2.5; Paratypes. IE-2007-1029 Madagascar, 14°29’S 47°26’E, 379– 332 m. Coll. Bouchet and Kantor, July 14, 2009 aboard N/ O Miriky CP 3289., 4 wet specs. R=8.7, r=2.8; R=9.2, r=2.9; R=8.7, r=2.9 . IE-2007-1172 , Madagascar, 12°31’S 48°15’E, 416 m. Coll. Bouchet, Puilandre, & Richer 27 June 2009. 2 wet specs. R=8.1 r=2.6; R=8.1 r=2.3 .

Figures

FIGURE 22. Mediaster roanae n. sp. Holotype IE-2007-1029. R=8.7, r=2.8 cm. A. Abactinal surface. Scale bar=3.0 cm. B. Closeup of abactinal surface. Scale bar=0.5 cm. C. Superomarginal, inferomarginal surfaces.Scale bar=0.2 cm. D. Actinal surface. Scale bar=3.0 cm. E. Furrow and adambulacral spination. Scale bar=0.2 cm.