Evoplosoma nuku, Mah, 2022

Mah, Christopher L., 2022, New Genera, Species and Occurrences of Deep-Sea Asteroidea (Valvatacea, Forcipulatacea, Echinodermata) collected from the North Pacific Ocean by the CAPSTONE Expedition, Zootaxa 5164 (1), pp. 1-75 : 46-47

Evoplosoma nuku n. sp.

FIGURE 15 A–G

Etymology. The species name is derived from the Hawaiian word “ nuku ” for “beak” alluding to the many jawshaped pedicellariae which adorn the surface. Noun is held in apposition.

Diagnosis. Body form strongly stellate (R/r=3.55), arms elongate. Abactinal, marginal and actinal surface covered by pointed irregularly shaped granules. Abactinal and actinal surface lacking large, prominent spines. Pedicellariae of two types present on the abactinal, marginal and actinal surfaces, including one showing slender beak-like valves as well as paddle-shaped valves. Marginal plate series both with prominent spines. Furrow spines 3 to 5, subambulacral accessories include one elongate proximal-facing pedicellariae and a thick, distal-facing blunt spine.

Comments. This species differs from E. forcipifera primarily in that is shows a more strongly stellate body form (R/r=3.5), the pointed irregular granules and the two types of pedicellariae observed. This includes the numerous beak shaped as well as the paddle-like pedicellariae. These pedicellariae, especially the elongate beak-like pedicellariae were observable from close-up video observations taken by the ROV ( Fig. 15F ). Color of this species was lighter than Evoplosoma forcipifera and displayed yellow to orange coloration on the disk.

This species also shares several characters with the South Pacific Evoplosoma tasmanica (McKnight 2006) in that it possesses a covering of evenly spaced, pointed granules present over the surface, lacking primary spines with pedicellariae present on the surface but differ in pedicellariae and abactinal plate morphology.

Occurrence: Johnston Atoll, 1603 m.

Description. Body strongly stellate (R/r=3.55), arms elongate, upturned. Disk arched, interradial arcs curved ( Fig. 15A, F )

Abactinal plates round to polygonal, abutted forming arched disk extending up to armtip. Surface flexible, covered by a dermal tegument with embedded granules, round, coarse, pointed, irregularly shaped, widely spaced ( Fig. 15B ). Majority of abactinal plates covered by two types of pedicellariae, One with large, elongate tong-shaped valves, and another with more broad, paddle-shaped valves, each up to 1.0 mm length projecting above the abactinal surface ( Fig. 15B ). Pedicellariae most numerous interradially adjacent to the superomarginal contact but absent from mid to distal arm plates but covering surface. Conical, blunt spines or tubercles present on a minority of abactinal arm plates as well as some plates adjacent to the madreporite. Madreporite polygonal, approximately 2.5 cm diameter, convex, flanked by five to six plates.

Marginal plates 36–38. Superomarginal interradial plates trapezoid in outline, becoming more elongate distally, with superomarginal plate series showing forming a distinct abactinal periphery around disk and basal arm regions, becoming more lateral-oriented medially to distally along the arm. Marginal plates larger interradially becoming smaller distally. Superomarginals and inferomarginals offset forming zigzag contact ( Fig. 15D ). Superomarginal surface tumid. Most superomarginal plates with a prominent, single, sharp, conical spine (2.0 mm length) projecting from the center of each plate ( Fig. 15B ), distal plates with spines becoming smaller and disappearing entirely adjacent to the arm tip. Superomarginal plate surface covered by pointed, angular granules, widely spaced ( Fig. 15D ). Each spine with one or more elongate, tong-like pedicellariae, with most sitting adjacent to the large centrally located spine. Interradial marginal plates mostly with one to three pedicellariae with second and third pedicellariae on plate edge adjacent to contact with abactinal and/or inferomarginal plate. Inferomarginal plates mostly with a single, prominent sharp conical spine similar to those on superomarginal plates. Spines absent interradially on two or three plates but covered with similar pointed, widely spaced, angular granules. One to four pedicellariae present per plate, identical to those on superomarginal plates, located near the base of each spine. Terminal plate elongate, trapezoid in outline, plate surface smooth, with two pronounced spines on the arm tip.

Actinal surface small ( Fig.15C ), two full plate series, with miscellaneous irregular plates. Individual actinal plates quadrate to irregular in shape. Surface covered by angular, pointed, coarse, widely spaced granules. Spines absent from actinal surface. Most actinal plates with one or two elongate beak-like and/or paddle-shaped pedicellariae ( Fig. 15C inset), identical to those on the abactinal surface present centrally on each plate. Actinal plates present only on disk, proximally on arm but absent from mid to distal arm regions ( Fig. 15C ).

Furrow spines three to five ( Fig. 15E, G ) quadrate in cross-section, blunt-tipped, rounded arranged in convex to straight arrangement, widely splayed out. Subambulacral accessories separated by a discrete space, composed of an elongate pedicellariae (facing proximally) and a blunt, round-tipped distally facing spine. Subambulacral spine becomes larger distally and occupies increasing portion of the subambulacral series extending to the arm tip. Remainder of adambulacral plate covered by coarse, pointed, angular granules identical to those on actinal surface ( Fig. 15E, G ). Oral plates with 15–16 blunt, spines with quadrate cross-section in broadly curved series. Oral plates each with a flattened, blade-like spine projecting into the mouth on each plate (two per interradius). Each oral plate half with a large, flattened, elongate pedicellariae, similar to those elsewhere. Remaining surface of oral plate with coarse, widely spaced pointed granules identical to those on actinal surface.

Color in life is bright orange. Pedicellariae were all open when observed in situ ( Fig. 15F ).

Material Examined. Holotype. USNM 1457372 Johnston Atoll, North Pacific Ocean. 15º28’N, 171º59’W, 1603 m, Coll. C. Mah & C. Kelley aboard NOAA Ship Okeanos Explorer, ROV Deep Discoverer. 22 July 2017. 1 wet spec. R =6.4 r=1.8. EX 1706_IMG_20170722 T 202139Z_ ROVHD.jpg.

Figures

FIGURE 15. Evoplosoma nuku n. sp. USNM 1457372. A. Abactinal view. Scale bar=5.0 mm. B. Abactinal-lateral view showing surface features. Scale bar=2.0 mm. C. Actinal view. Scale bar=5.0 mm. Inset showing pedicellariae and surface features. Individual pedicellariae=1.0 mm length. D. Lateral view showing features of the superomarginal and inferomarginal plates. Scale bar=3.0 mm. E. Adambulacral armature showing furrow and subambulacral spines. Scale bar=2.0 mm. F. In situ observation, Johnston Atoll, 1603 m. G. Actinal surface showing off plate shape, surface features. Scale bar=2.0 mm.