Ceramaster vorax, 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 : 39-42

Ceramaster vorax n. sp

FIGURE 13 A–F

Etymology: This species is named for the predatory behavior it was engaged in while it was collected ( Fig. 13A ).

Diagnosis. Body weakly stellate (R/r=1.71). Arms triangular, interradial arcs weakly curved Abactinal plates hexagonal to round in outline. Abactinal plates tabular each covered by approximately 18–40 granules, mostly 20–26. Peripheral granule approximately three to five times the size of the central granules. well developed fasciolar groove. Superomarginals 18–20 per interradius (armtip to armtip), inferomarginals 22–24. Superomarginal plates covered by coarse, round close-set but evenly distributed granules, 300–700, with approximately three to four present along a 1.0 mm line. Superomarginal plate surfaces with a distinct but irregularly shaped bald spot, ranging from small oval to large quadrate with rounded edges, encompassing the entire plate present on all superomarginal plates. Bald spot absent from granule-covered inferomarginal plate surface. Furrow spines, four to seven (mostly six), two to four subambulacral spines, each approximately twice the size of the furrow spines. Tong-shaped pedicellariae present on the actinal surface.

Comments. This species displays abactinal morphology with trapezoidal peripheral granules that are three to five times larger than the central, rounded granules on each tabular plate. The trapezoid peripheral granule is shared with several other species, most notably the widely occurring Ceramaster patagonicus ( Sladen 1889) and other potentially related species such as the Indian Ocean Ceramaster mortenseni Koehler 1909 and the south Pacific Ceramaster australis . However, the peripheral abactinal granules in these species are closer in size to the central granules and are only about twice as large as the central granules. Characters observed in C. vorax n. sp., such as the furrow and subambulacral spine and morphology, presence of pedicellariae, as well as the broader marginal plate shape in C. patagonicus support this specimen as representative of a separate but undescribed species.

In situ Observation. This species was encountered with its abactinal surface inflated and the majority of its disk hunched over and feeding on what was apparently the demosponge, Poecilastra sp, ( Fig. 13A ). The individual’s stomach was weakly extended based on observations immediately following collection. Examination of the gut contents indicated a remnants of an unidentified, granular soft tissue, perhaps that of the sponge.

Occurrence: Johnston Atoll, 491.9 m.

Description. Body weakly stellate (R/r=1.71). Arms triangular, interradial arcs weakly curved ( Fig. 13B ). Abactinal surface inflated, presumably swollen with water ( Fig. 13A ). Armtips upturned.

Abactinal plates tabulate ( Fig. 13 B-inset). Abactinal plates hexagonal to round in outline. Each plate with well developed tabulae overhanging the shaft, fasciolar grooves well-developed. Papulae present radially and interradially but gradually pinching out distally along the interradii adjacent to the superomarginal plates. Abactinal plates relatively homogeneous in size but smaller, more crowded and more angular, becoming diamond shaped, interradially. Radial regions swollen with relatively thin abactinal body wall, interradial regions depressed with more crowded abactinal plates along each interradius ( Fig. 13B ). Abactinal plates present along arm up until first superomarginal plates abut against one another along the radius. Abactinal plates each covered by approximately 18–40 granules, mostly 20–26. Radial and proximal plates bearing 12–24 large angular granules, approximately 2–8X the size of the central granules, 7–30, each round in outline with granular number increasing distally along the arm. Granules are smooth, convex in curvature. Distal arm plates also show more comparably sized smaller peripheral versus central granules versus those proximally which are more angular and disproportionately sized.Abactinal plates interradially with least disparity in size/shape relative to those present along radial regions. Abactinal plates present distally, especially adjacent to superomarginals on arm, very small and homogeneous compared to those on disk. Madreporite convex quadrate in shape with four abactinal plates in contact, but with approximately 15 abactinal plates forming close-set arrangement around madreporic region. Small (approximately 1.0 mm wide) paddle-shaped pedicellariae observed on two distally located abactinal plates. Small (1.0 mm wide) paddle-shaped pedicellariae

Superomarginals 18–20 per interradius (armtip to armtip), inferomarginals 22–24. Superomarginals and inferomarginals offset with zig-zag contact between them. Superomarginals inferomarginals quadrate in outline. Superomarginal plates covered by coarse, round close-set but evenly distributed granules, 300–700, with approximately three to four present along a 1.0 mm line. Peripheral granules only slightly larger forming linear series around the periphery of each plate, approximately 20–30 along each side. Superomarginal plates convex becoming more strongly convex distally. A distinct but irregularly shaped bald spot, ranging from small oval to large quadrate with rounded edges, encompassing the entire plate present on all superomarginal plates ( Fig. 13D, E ). These bald spots devoid of granules, are weakly raised surfaces on the surface of the superomarginals. Distalmost plates adjacent to the terminal plate are especially tumid ( Fig. 13D ). Inferomarginals are more elongate in shape with an identical cov- er of granules (300–700) on the plate surface continuously intergrading with those on the actinal surface. Bald spots largely absent from inferomarginal plates save for those present on distalmost plates adjacent to the terminal plate ( Fig. 13C ). Distalmost 2nd and 3rd pairs of superomarginals abutted at angles, unevenly in contact along different plate sides ( Fig. 13D ). Enlarged peripheral granules along superomarginal/inferomarginal contact from zigzag edge along weakly developed fasciolar groove between the marginal plate series. Terminal plate triangular, smooth.

Actinal surface with seven to eight well-defined chevron rows ( Fig. 13C ). Individual actinal plates hexagonal, each covered by widely spaced round to angular granules, approximately three along a 1.0 mm line. Inferomarginals form a discontinuous boundary with actinal plates which have a series of larger granules bordering the discontinuity. Furrow spines four to seven, mostly six to seven proximally, arranged in a convex palmate to straight pattern ( Fig. 13F ). Spines are most abundant proximally, decreasing in number distally. Furrow spines are blunt and quadrate in cross-section with rounded tips. Subambulacral spines two to four, flattened with round, blunt tips ( Fig. 13F ). Subambulacral spines closest to furrow spines are twice as thick as furrow spines and approximately 10% taller than furrow spines. Subambulacral spines closer to actinal surface decrease in size to granules comparable in size to those on actinal plate surface. Granules on actinal/adambulacral surface obscure the boundary between adambulacral and actinal plates. Small paddle-shaped pedicellariae (length about 1–2.0 mm) present in alveolar pits along plate series adjacent to adambulacral plate series, approximately three to four per interradius ( Fig. 13F ). Oral plates with 12–15 spines, flattened but triangular in cross-section with tallest spines projecting into mouth. Oral plates with 2 paired series of 7 short, blunt spines forming a contact between the oral plates. Remaining oral plates surface with three quadrate shaped, blunt spines in addition to six to nine short, blunt spines. Remainder of oral plate surface bare.

Well developed pyloric caeca was observed through the broken body wall.

Color in life was yellow with dark orange highlights ( Fig. 13A ). Bald spots on superomarginal plates and interradial folds were dark orange.A ring of plates around the primary circlet was weakly colored orange.Actinal surface was white.

Specimen was damaged during collection.

Material Examined. Holotype. USNM 1457352, Johnston Atoll, North Pacific Ocean. 16º44’N 169º22’W, 492 m, Coll. C. Mah & C. Kelley aboard Okeanos Explorer using ROV Deep Discoverer , 15 July 2017, EX 1706. 1 wet spec. 1 wet spec. R =4.8 r=2.8.

Images Examined

Wake Atoll, Wake Island region, 18.47087809, 166.6810625, 1407 m EX1606 _IMG_20160812 T014052 Z_ ROVHD _COR_ ASR.jpg

Bank 9 South, Hawaiian Islands, 26.83053592, -175.6069087, 1083 m EX1504 L2_IMG_20150810 T023747 Z_ ROVHD _ SPO _ ASR.jpg

Figures

FIGURE 13. Ceramaster vorax n. sp. USNM 1457352. A. In situ observation of holotype feeding on sponge, Johnson Atoll, 492m. B. Abactinal view. Scale bar=5.0 mm. Inset showing close-up of abactinal plate. Individual plates =1.3 mm diameter. C. Actinal view. Scale bar=5.0 mm. Specimen damaged during collection. D. Armtip showing abactinal arm plates, distalmost superomarginal plates. Scale bar=3.0 mm. E. Abactinal view showing superomarginal plates. Scale bar=3.0 mm. F. Close-up of furrow adambulacral spination, including furrow spines and subambulacral spines. Scale bar=2.0 mm.