Atheraster symphonia, 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 : 28-31

Atheraster symphonia n. gen. n. sp.

FIGURE 9A–F

Etymology: The species epithet symphonia is Greek for “symphony” alluding to the collection locality for this species from the Musicians Seamounts in the North Pacific.

Diagnosis. Strongly stellate body (R/r=3.85), elongate arms. Abactinal and actinal plate surfaces covered by continuous layer of coarse granules. Superomarginal and inferomarginal plates with conical spines, 1–3 but surface is otherwise smooth. Furrow spines, 8–12. Paddle-shaped pedicellariae present on adambulacral plate.

Comments. This species shares one very distinctive character with Atheraster arandae Mah 2006 , notably the conical spines on the superomarginal and inferomarginal plates in linear series as well as sharing similar body form with elongate arm and disk shape. Furrow spine number, 8–12 overlaps slightly with those in C. arandae (12–15).

Atheraster symphonia n. sp. differs in that the abactinal surface is covered by large, angular, granules which form both the periphery of the large, flat abactinal plates, but also the abundant covering accessories on the disk and arm surface ( Fig. 9B ). Interradial spines on C. arandae occur as a cluster whereas those on C. symphonia only number one to three ( Fig. 9B ). The larger granules on this species are also more evident on the arms which show more heavily the coarse, angular granules as opposed to C. arandae which primarily shows the enlarged bare, smooth arm abactinal plates.

Feeding Observations. The holotype for this species was observed and collected feeding on what appeared to be a chrysogorgiid octocoral. Other similar looking species were observed feeding on isidid octcorals (“bamboo corals”) but owing to A. symphonia ’s superficial resemblance to Atheraster arandae it is unclear if this represents feeding variation within one species or species-specific feeding behavior on different octocorals.

Worm Commensal/Kleptoparasite/Predator? One observation from Vogt Seamount showed two yellow scale worms with several lobate projections, one several times larger than the other, present on the surface of the observed Atheraster symphonia n. sp. individual. The individual in this image showed a marked discoloration on the abactinal surface. This suggests a number of possibilities, including predation or possibly some kind of epidermal irritation as a consequence of the worm’s presence on the animal’s surface.

Occurrence: North Pacific, Sibelius Seamount (Musicians Seamounts), 27.25, -160.63 (27º15’N, 160º38’W), 2437.1 m.

Description. Body strongly stellate (R/r=3.85), arms narrow, elongate, disk surface swollen, interradial arcs curved ( Fig. 9A ).

Abactinal surface composed of abutted plates, circular to irregularly round. Disk plates similar in size, arm plates twice the size of those on the disk. Abactinal disk plates extend from disk to about 75–80% along arm, stopping short of the distalmost segment of each arm ( Fig. 9D ). Disk plates flat, flush with abactinal surface, arm plates strongly convex, several plates on primary circlet and irregularly along carinal series approximately twice to three times the size of the disk plates. Enlarged carinal plates either adjacent or alternating with two to four coarse granules. Smaller, bald plates present interradially, with granules easily constituting 50%–75% of the total diameter of the plate+granules. Where bald, smooth plates are not present, abactinal surface covered by quadrate to polygonal, coarse granules. Granules abundant, 3 to 4, counted along a 1.0 mm line. Individual plates with 13–30 granules form periphery around each of the large, flat bare plates ( Fig. 9B, D ). Granules large, occupying 25–33% of the total diameter of the plate surface+granules. Interradial regions, especially adjacent to superomarginals covered by densely packed, abundant granules. Madreporite strongly convex, appearing dome-like with well-developed sulci ( Fig. 9B ). Papulae present in twin series adradially on disk but absent from disk radii and along the arm radii, and from each interradius. Papulae each flanked by five to seven coarse granules. Arms with enlarged, bald, convex plates, two to four times the size of those on the disk but each with a periphery of large, coarse polygonal to quadrate granules ( Fig. 9D ). A minority of these large arm plates at the arm base with mostly a single, or on one place two smaller, central tubercle(s). Transition between bald disk plates to arm plates is gradual. Large peripheral granules between abactinal plates forming a mosaic. Pedicellariae paddle-like, limited to less than a dozen plates, each valve with three to four finger-like projections.

Marginal plates 58–62, plates wide especially interradially with distinct lateral facing becoming with a more abactinal facing from the midpoint to distally along the arm ( Fig. 9A, C ). Superomarginals each with a single, large, conical sharp spine present centrally on each plate ( Fig. 9B, D ). One or two interradial superomarginal plates with two, short spines. Spines absent on the distalmost superomarginal plates, approximately 10–15 plates from terminus. Spines form a distinct linear series along dorsolateral and ventrolateral angles of superomarginals and inferomarginals. Superomarginal plate surface bare, smooth with no accessories. Each superomarginal plate with approximately 40–60, rounded polygonal granules, approximately 10–15 per side. Superomarginals mostly 1:1 with inferomarginals becoming more offset distally creating a more zig-zag contact between the two plate series. Inferomarginals interradially with two to six spines present centrally, with one single large spine present on remainder of inferomarginals disappearing on the distalmost five to 10 plates away from the terminus. Interradial spines much smaller, less than 30% of the height of the large, central plates with some displaying a more tubercle-like appearance. Inferomarginal spines with deep notches present on the spine-tips interradially and along basal regions on arms. Inferomarginal plates bare, smooth with one to three plates displaying one to four widely spaced circular granules on the plate surface. Pedicellariae similar to those on the abactinal surface, with three finger-like projections, small, present on one to four inferomarginal plates. Peripheral polygonal granules present between superomarginal and inferomarginal contact with granules forming a third layer between the other two plates along the lateral contact. Terminal plates round, about the size of 3 or 4 plates. Surface smooth with no surface decoration. Superomarginals abutted along mid-radius for approximately 8 to 12 distalmost plates.

Actinal surface relatively small, composed of two to three full series with only three to six irregular plates present distally at actinal-inferomarginal contact ( Fig. 9C, F ). Individual actinal plates variably triangular, polygonal to quadrate in shape, each distinctly separated by shallow fasciolar grooves. Actinal plate surface covered by four to 10 (mostly 6 to 8), pointed granules, each widely spaced from one another ( Fig. 9F ). Some actinal plate surfaces bare, without granules. Approximately 40–50% of the actinal plates with a large, short, spine-like granule present centrally on each plate, each with notched tips ( Fig. 9F ). One proximal plate per actinal interradius with a large palm-shaped pedicellariae with three to four finger-like projections. Actinal plates present on disk, not extending along arm.

Furrow spines 8–12, ( Fig. 9E ) fewer furrow spines proximally increasing after first two adambulacral plates. Individual furrow spines sharply quadrate in cross-section, spines in linear series.Individual spines with fine, needle-like projections emerging from furrow-spine tips. Adambulacral plates rectangular in shape. Subambulacral armament composed of a large, paddle-shaped pedicellariae, proximal facing, valves with four to six tooth-like projections and a large notched spine (distal from mouth), both structures set off from furrow spines by a large, discrete space ( Fig. 9E ). Subambulacral spines double to triple in length at 50% of arm length distally.Adambulacral plates with eight to 15, mostly 10–12 pointed angular granules, widely spaced. Furrow spines on oral plates, 18, similar to furrow spines on other adambulacral plates. Oral plate surface covered by low, angular granules, 25–35 on each half, approximately 8 or 10 granules form symmetrical boundary on each side of the sulcus formed by the two oral plate halves.

Color in life a solid, orange abactinal surface. Oral surface lighter orange to yellow ( Fig. 9F ).

Material Examined. Holotype. USNM 1467555 Sibelius Seamount, 27.25, -160.63 (27º15’N, 160º38’W), 2437 m. Coll. M. Putts, 11 Sept. 2017 EX 1708 , dive 4. 20170911/010427. 1 wet spec. R =8.1 r=2.1

Images Examined

Vogt Guyot , Marianas Islands region, 19.80357096, 148.4464295, 1822 m EX1605 L3_IMG_20160705 T235544 Z_ ROVHD _ ASR _COR_HL.jpg (with worm)

McDonnell Guyot , Wake Island region, 19.14592803, 164.5610819, 2497 m EX1606 _IMG_20160805 T024825 Z_ ROVHD _ ASR _ AUD.jpg (Feeding on Isididae )

Figures

FIGURE 9. Atheraster symphonium n. sp. Holotype. USNM 1467555. A. Abactinal surface. Scale bar=10.0 mm. B. Abactinal-lateral, showing spines on marginal plates. Scale bar=3.0 mm. C. Actinal surface. Scale bar=10.0 mm. D. Abactinal surface showing transition of plate size between disk and arm. Scale bar=3.0 mm. E. Furrow spines showing pedicellariae and adambulacral/actinal accessories. Scale bar=3.0 mm. F. Close-up of actinal surface showing intermediate regions and furrow spines. Scale bar=3.0 mm. G. In situ image of holotype, Sibelius Seamount, Musicians Seamounts, 2437 m.