Eknomiaster horologium, 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 : 34-35

Eknomiaster horologium n. sp.

Figure 11 A–E

Etymology. The species epithet, horologium is Greek for “hourglass” referring to the hourglass-like shape formed by the outlines of the actinal pedicellariae which are indicative of this species.

Diagnosis. A species identified by penultimate superomarginal plates which are consistent in size with others in the series ( Fig. 11A ), hourglass shaped actinal pedicellariae ( Fig. 11D, E ), and two to four furrow spines per plate.

Comments. Several abactinal and marginal characters in this species are identical with those in the South Pacific Eknomiaster macauleyensis including an identical number of shape, and appearance (i.e. granules absent, etc.) of marginal plates, as well as very similar abactinal plates.

The penultimate superomarginal plates in this species appears intermediate relative to South Pacific members of Eknomiaster macauleyensis , which variably display both enlarged, triangular penultimate superomarginals (in the New Zealand type) and smaller penultimate superomarginals consistent in series with the other superomarginal plates as observed in the New Caledonia specimens.

The actinal surface and adambulacral armature however differ significantly. Furrow and adjacent subambulacral spines in Eknomiaster horologium n. sp. numbering three or four and two or three respectively versus the seven or eight furrow spines in the South Pacific individuals. Pedicellariae are immediately adjacent to the furrow spines in the New Zealand individuals whereas the New Caledonia individuals possess four to five subambulacral spines directly adjacent to the furrow spine series. Also distinctive is the size and morphology of the pedicellariae in Eknomiaster horologium n. sp. which, when seen in broad outline within its actinal concavity appears hour-glass like in shape. The valves on these pedicellariae are much smaller, and curved relative to pedicellariae in the South Pacific members, which display much broader and quadrate shaped pedicellariae valves.

Occurrence. Northeast of Glorioso Island, western Indian Ocean. 583– 614 m.

Description. Body stout, weakly stellate (R/r=1.55) in shape, arms triangular in outline. Interradial arcs weakly curved to straight ( Fig. 11A ). Arms upturned.

Abactinal surface concave. Plates abutted, polygonal to round in outline, with distinct plate boundaries. Primary circlet distinct with distinct, large primary plates and smaller interradial plates adjacent to contact with superomarginal plates ( Fig. 11A, B ). Plate surfaces bare and smooth with no surficial accessories. Each plate with small, homogeneous quadrate shaped peripheral granules, 24–90 evenly distributed around edge of each plate. Plates restricted to disk with none extending beyond point on arms where superomarginals abut over midline. Madreporite triangular, flush with well-developed sulci, flanked by three abactinal plates. Pedicellariae not observed from abactinal surface.

Superomarginal plates mostly eight, with variably nine on one side ( Fig. 11A ) from arm tip to arm tip. Inferomarginals eleven. Superomarginals and inferomarginals show stronger correspondence interradially but demonstrating more offset distally as the inferomarginals show stronger jagged contact relative to the superomarginals. Superomarginal plates with two to three plates abutted over midline resulting in jagged contact between plates adjacent to the terminal. On three arms, a triangular superomarginal is present. Interradial superomarginals wider, with convex surface with more distal superomarginals more elongate. Superomarginal and inferomarginal surfaces bare and smooth with no surficial characters ( Fig. 11C ). Inferomarginals with distinct convex contact with actinal surface. Peripheral granules quadrate, approximately 40 to 120 per plate, closely arranged, numbering approximately 10 to 30 per side. but small and flattened relative to other granules. Terminal plate triangular with smooth surface. No pedicellariae.

Actinal plates in approximately three complete rows with a single incomplete row sitting adjacent to the inferomarginal contact ( Fig. 11D ). Each plate quadrate to polygonal in shape. Each plate displays a large, prominent paddle-shaped pedicellariae with each valve displaying five or six distinct teeth which are in turn braced by a pair of four square-shaped ossicles located at the base of each pedicellariae valve ( Fig. 11D, E ). Each pedicellaria sits in a pit devoid of granulation on the surface around it. Immediately surrounding each pedicellaria in a convex pattern are two to 60 polygonal granules on the central surface of the plate. A minority of actinal plates lack pedicellariae, in which case granules alone cover the surface of the actinal plate with no “pedicellariae base ossicles.” Around each actinal plate is a series of peripheral granules, each polygonal in outline and closely arranged, approximately one to 48, but mostly 20–40 around each plate. At the apex of each actinal region, two pedicellariae sit on a single oval-shaped plate ( Fig. 11E ).

Furrow spines three proximally, four distally each spine blunt tipped, cylindrical in cross-section ( Fig. 11E ). Subambulacrals two or three, blunt tipped, with each spine as thick as each furrow spine. Furrow and subambulacral spination crowded but each spine series separated from one another by a distinct space. Adambulacral plate with three irregular rows containing three to six, widely spaced, angular granules. Oral plate with eight thick, blunt spines, each consistent in thickness, height with furrow spines. Spines proximal-most to the oral plate apex flattened and scoop shaped. Blunt wide spines projecting into oral region from tip of oral plate. Oral plate divided centrally by distinct sulcus with distinct series of nine angular granules decreasing in size from proximal to distal. Angular granules, 18–20, evenly distributed, cover the remainder of each side of the oral plate

Material Examined. Holotype. IE-2013-17168 , Northeast of Glorioso Island , 11° 30'S, 47° 29' E to 11° 29 'S, 47° 29' E, 614– 583 m. Coll. S. Samadi et al. BIOMAGLO DW 4813 25 Jan 2017, 1 wet spec. R=3.1 r=2.0

Figures

FIGURE 11. Eknomiaster horologium n. sp. Holotype IE-2013-17168. R=3.1, r=2.0 cm. A. Abactinal surface. Scale bar=1.0 cm. B. Closeup of abactinal plates. Scale bar=0.3 cm. C. Lateral view showing inferomarginal and superomarginal plates. Scale bar=0.3 cm. D. Actinal surface showing pedicellariae distribution. Scale bar=1.0 cm. E. Furrow spines and pedicellariae on actinal surface. Scale bar =0.3 cm.