Wallastra elenderae, 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 : 98-100

Wallastra elenderae n. gen. n. sp.

Figure 37 A–G

Type species. Wallastra elenderae n. sp. by monotypy.

Etymology. This genus and species are named for dear friend, opera singer, and co-author of the textbook Introductory Physics, Ms. Elender Wall (1969–2016).

Diagnosis. Body strongly stellate (R/r=3.46) with elongate, slender arms, weakly curved interradial arcs ( Fig. 37A, F ). Abactinal plates bare, surface mostly bare and smooth ( Fig. 37B ), especially on distal disk regions adjacent to superomarginals and along arms. Central disk plates with one to several, widely distributed button-like granules. Superomarginals wide to quadrate in shape, with mostly bare surface, or widely distributed coarse granules occur ( Fig. 37D ). Each actinal plate covered with closely articulated granules, most plates with a single large bivalve pedicellaria ( Fig. 37E ). Furrow spines four or five ( Fig. 37G ).

Comments. Based on comparisons with other goniasterid taxa, the species described here cannot be easily reconciled with known goniasterid genera, and therefore the new genus Wallastra is recognized.

Wallastra n. gen. lacks the crystalline tubercles embedded in the surface of the abactinal plates, which identifies all species of Astroceramus as well as the superomarginals abutted over the radius of each arm. Most species of Astroceramus also possess one or two enlarged subambulacral spines that are absent from Wallastra .

Abactinal plates on Wallastra n. gen. possess one to approximately eight to 10 coarse granules embedded in the plate surface but are otherwise bare and smooth. Granules abruptly disappear on arm plates where abactinal plates become flatter and are entirely devoid of surficial accessories. This character is reminiscent of the abrupt change between plates that defines the difference between Circeaster and Lydiaster . In Circeaster , abactinal arm plates are abruptly larger whereas those in Lydiaster remain relatively similar in size on the arm and disk. However, Lydiaster possesses much larger and wider marginal plates with a stronger abactinal facing, a thicker and more stout body shape and widespread spinelets that are absent from Wallastra n. gen. Two species of Circeaster , C. sandrae (South and Central Pacific) and especially C. pullus (North Pacific) display similar abactinal and marginal plate patterns to both Wallastra n. gen. and Astroceramus .

Occurrence. Solomon Islands and Western Indian Ocean , between Mayotte and the Glorioso Islands , 550–836 m.

Description. Body strongly stellate (R/r=3.46), arms elongate, tapering. Interradial arcs weakly curved to nearly straight ( Fig. 37A ).

Abactinal surface flat, composed of round to polygonal abutted plates ( Fig. 37A, B ), which are flush with superomarginal plate surface ( Fig. 37D ). Approximately three rows of abactinal plates (at R= 10.4 cm) extending along arm to terminus ( Fig. 37C ), decreasing in number to a single row of wide then very narrow, irregularly shaped, strongly convex plates along distalmost arm region. Plates largest and most polygonal along papular (radial regions) with smallest and most irregular plates occurring interradially. Plates with discrete peripheral row of quadrate to polygonal shaped granules,12–30, mostly 15–25, with approximately four to five granules present per side ( Fig. 37B ). Peripheral granules largest on disk occupying 1/3 to 1/5 of the total width of each plate becoming substantially smaller on arm plates, occupying only approximately 1/6 to 1/10 of the total plate distance. Peripheral granules on arm more rounded and nearly flush with plate surface versus those on disk which are raised and sit above the plane of the abactinal plate surface. Abactinal plate surfaces on the disk possess one to 15 (mostly two to six) large, coarse widely spaced granules but are otherwise smooth, bare and are mostly devoid of other structures or accessories. Granules are widely spaced on all but the plates flanking the polygonal shaped madreporite. Of the seven plates which flank the madreporite, four possess abundant and closely spaced coarse granules all but covering the plate surface. This side of the madreporite with granule-covered plates with one to two irregularly spaced rows of plates with similarly abundant granule-covered plates. Two plates observed each with a large paddle-shaped pedicellaria (approximately 1.5–2.0 mm width) present in the center of each plate. These large coarse button-like granules decrease in number farther away from the center of the disk, disappearing completely on the disk edge, arm base and along the surface of the arm plates. The absence of the button-like granule leaves a distinct concavity on the plate where it has been removed, otherwise the surface is flat and smooth. Papulae were extended on specimen examined with six numbering around each plate along radial regions at the base of each arm extending from the radial region of the disk.

Superomarginal and inferomarginal plates, approximately 62–66 per interradius. Plates wide, quadrate in shape with flattened surface interradially but becoming more elongate and tumid distally, becoming much more strongly convex adjacent to arm tip. Superomarginals and inferomarginals with 1:1 correspondence interradially becoming more offset distally, showing a more zigzag contact along the arm. Distalmost three to four superomarginals abutted over midline. Superomarginals with one to approximately 25 coarse, round button-like, widely spaced granules present on each plate surface, granules are most abundant interradially, gradually decreasing and then disappearing completely along plates present on the arm ( Fig. 37D ). When removed, disk granules leave a distinct, concave pitting on the superomarginal plate surface. Inferomarginal plate surfaces show same general pattern but interradial plates also possess a dense row of coarse, polygonal granules identical to those which compose the peripheral granule layer around the marginal plates ( Fig. 37D ). Peripheral granules around superomarginals, polygonal to narrowly quadrate, approximately 30–80, mostly 40–60 forming (15 per edge) narrow border around superomarginal plates becoming nearly indistinct near arm terminus. Peripheral granules around inferomarginals similar in size and number except for those in contact with granules on the actinal plate surface, which are slightly larger than those on the other sides of the inferomarginal plate. Granules on the inferomarginal/actinal plate contact are much larger, coarser, in close contact, and similar in overall appearance. As with superomarginals, granules are most numerous interradially, with numbers decreasing and disappearing entirely on inferomarginal plate surface along the arm, especially distally adjacent to the arm terminus. Terminal plate is large, triangular in shape, approximately the size of four adjacent superomarginal plates, with bare surface and a large blunt spine on the tip.

Actinal surface composed of approximately three full series in chevron-like pattern, with irregular incomplete series adjacent to contact with inferomarginal plates ( Fig. 37E ). Actinal plates quadrate to polygonal in outline, all plates on disk covered by coarse, closely distributed polygonal to round granules, four to 12 per plate. Approximately 1 granule counted along a 1.0 mm line. Actinal plates along arm with decreasing number of granules, in some cases disappearing from plate surface. Large (1.0–2.0 mm wide) trapezoid shaped pedicellariae ( Figs. 37E, G ), each with short, jagged complimentary valves, numbering one per plate, occurring on approximately 50% of actinal plates, variably present throughout each interradius.

Furrow spines four in a linear series increasing to five distally, quadrate to triangular in cross-section with spines flattening out farther along arm, becoming individually narrower and more prominent ( Fig. 37G ). Variably, some spines are flattened and are more wedge-shaped. Furrow spines mostly blunt and smooth but most proximal spines with notches or some texturing on each spine tip. Furrow spines are set off by a discrete space, then two to four short triangular to rounded subambulacral spines, less than 25% of the length of each furrow spine. When only two subambulacrals are present, they occur on either side of the adambulacral plate, flanking a large bivalve pedicellaria with large rectangular valves with jagged tips, similar to those on actinal surface ( Fig. 37G ). Subambulacral spines transition from two short enlarged granules to a single enlarged blunt spine on distalmost adambulacral plates. Subambulacral pedicellariae occur in a continuous series along the adambulacral plates on the disk but gradually disappear along the transition from disk to arm. Pedicellariae are in turn, flanked by a row of three, large, blunt spines, quadrate to rounded in cross-section, which are two to three times as thick as the adjacent actinal granules. Pedicellariae set off from both the furrow spines and the thickened subambulacrals by discrete bare spaces. Pedicellariae are absent on a minority of plates, and are replaced by a series of two to four small polygonal granules similar to those on the actinal surface. Remainder of adambulacral surface covered by four to 20 thick, mostly 10 to 15 polygonal granules, best developed along arm after pedicellariae series has terminated.

Oral plates with six to eight thick spines, ranging from thickened quadrate to flattened and triangular in crosssection with thin, flattened paddle like spines projecting into oral region from each paired oral plate. Oral plates with four or five thick subambulacral spines, each two to four times as thick as the furrow spines with six to eight, short paired, irregular, triangular granules on each side of the oral plate contact along the midline.

Color in life, disk is light orange with darker orange arms and solid dark marginal plates.

Material Examined. Holotype: MNHN-IE-2013-17165. Western Indian Ocean , between Mayotte and the Glorioso Islands, 12° 18 'S, 46° 27' E to 12 ° 17 'S, 46 ° 28' E, 842– 836m, Coll. S. Samadi et al. BIOMAGLO DW 4792 , 22 Jan 2017, leg 1. 1 wet spec. R=10.4 r=3.0. Paratype: IE-2007-1291 . Solomon Islands 8°16’S 160° 43’E, 550 m, Coll. Richer & Boissellier, 15 Sept. 2007. N/ O Alis, SALOMONBOA 3 DW 2792 1 wet spec. R=9.3 (arm twisted) r=3.2

Figures

FIGURE 37. Wallastra elenderae n. gen. n. sp. Holotype IE-2013-17165. R=10.4, r=3.0 cm. A. Abactinal surface. Scale bar=3.0 cm. B. Closeup on abactinal plates. C. Closeup showing arm, transition between disk and arm abactinal plates. Scale bar= 1.0 cm. D. Lateral view of superomarginal and inferomarginal plates and surface. Scale bar=0.5 cm. E. Oral surface close up.Scale bar=3.0 cm. F. Oral surface. Scale bar=3.0 cm. G. Furrow and adambulacral spination, pedicellariae and granulation. Scale bar=1.0 cm.