Okeanosaster, 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 : 61-64

Okeanosaster hohonui n. gen, n. sp.

FIGURE 21A–G

Etymology: Okeanosaster honors the NOAA Ship Okeanos Explorer. The species epithet “ hohonu” is the Hawaiian word for “deep” and alludes to the great depth where this species was collected.

Diagnosis. Body stellate (R/r=2.2), interradial arcs straight.Abactinal, superomarginal and inferomarginal plate surfaces smooth with no surficial accessories. Abactinal plates creating a bumpy surface, extending to armtip. Polygonal granules, 4–20 small polygonal granules present around each plate periphery. Superomarginal plates, 20–22 armtip to armtp with abactinal plates extending to arm terminus.Actinal surface covered by granules. Furrow spines five or six. Subambulacral spines two to four.

Comments. Okeanosaster hohonui n. gen. n. sp. was observed primarily on basalt, mostly very solid lava flows and Mn covered substratum. One observation of this species from the Johnston Atoll region (EX1706_IMG_ 20170728T203756Z_ROVHD.jpg) showed in hunched over an unidentified colonial cnidarian.

This species shares several characters with other members of the Goniasteridae that possess smooth marginal plate surfaces, lacking any deciduous or surficial granules. This includes Iconaster , Glyphodiscus and related taxa such as Lithosoma and Pontioceramus (Mah 2005) as well as multiple genera within the Pentagonasterinae (Mah 2007).

Glyphodiscus and Iconaster are completely devoid of granules on the abactinal, marginal and actinal plate surfaces. These genera differ from Okeanosaster n. gen., which has granules covering the actinal surface. Lithosoma is similar overall to Iconaster and Glyphodiscus but has glassy granules embedded in the abactinal plates as well as a much more strongly stellate shape which are absent in Okeanosaster . Lithosoma , Glyphodiscus and Iconaster also possess superomarginal plates which form a wide, distinct perimeter around the disk and along the arm (Mah, 2005) that are absent in Okeanosaster which has more lateral-facing marginal plates. Pontioceramus has a dense covering of granules on the actinal intermediate plates as well as a wide superomarginal plate perimeter and a much broader disk than Okeanosaster .

Among the Pentagonasterinae, Tosia and Pentagonaster possess shallow fasciolar grooves among the abactinal plates, lack granulation on the actinal surface and demonstrate much larger (and thus fewer) marginal plates than Okeanosaster . Okeanosaster does not display the intermarginal granulation and tubercle-like spination on the abactinal and marginal plates as observed on Ryukuaster . Anchitosia displays some similarities with Okeanosaster in that it also has smooth abactinal, marginal and actinal plate surfaces but differs in having flat or weakly convex abactinal plates, much larger peripheral granules around the abactinal and actinal plates and much larger (and thus fewer) marginal plates than Okeanosaster .

Okeanosaster also invites comparison with the Antarctic goniasterid Pergamaster , with which it shares smooth abactinal and marginal plates and a granule-covered actinal surface. However, abactinal plates in Okeanosaster n. gen. are much more strongly convex, peripheral granulation is smaller than in Pergamaster and actinal spination and accessories are significantly smaller and dissimilar in shape and distribution. Furrow spination in Pergamaster is also substantially larger with individual spines easily 2 to 3X the width and length of those in Okeanosaster .

Occurrence: Musician Seamounts, Marianas Islands region, central Pacific ( Howland Island), Johnston Atoll region. 1743–3304 m.

Description. Body stout, stellate in outline (R/r=2.22) with triangular arms, broad to straight interradial arcs. Disk strongly convex, arms thick ( Fig. 21A ).

Abactinal plates abutted, mostly round to polygonal in outline. Plates mostly strongly convex to flat, creating a heterogeneous bumpy surface appearance ( Fig. 21A, B ). Abactinal plates smooth with no surficial accessories. Plate sizes heterogeneous, mostly larger plate with smaller, secondary plates approximately 10% of the size of larger plates. Abactinal arm plates extend to armtip ( Fig. 21D ) more strongly convex than those on disk and approximately 10–25% larger than those on disk. Polygonal granules, 4–20 small polygonal granules present around each plate periphery. Papulae, three to seven, pores present only on limited radial disk regions, otherwise papulae absent from arms and disk, especially interradially. No pedicellariae observed.

Superomarginal plates, 19–20, inferomarginals, 21–22 per interradius. Both series correspond 1:1, especially interradially becoming more offset along arm, forming zigzag contact between the two series distally. Superomarginal plates most quadrate with angular corners becoming narrower distally along the arms ( Fig. 21E ). Some superomarginal plates irregular in size, shape, interrupting regular series along arm. Superomarginals convex, lateral angles curve. Superomarginal plate surface bare, smooth with no surficial accessories (no granules, etc.) ( Fig. 21D, E ). Inferomarginal plate plate surface bare, smooth laterally, actinal surface with widely spaced round granules present. Superomarginals form approximately 22% (0.2/0.9) of disk radius, “r”, but take up to 50% of distance across arm width. Granules, small, polygonal, approximately 15 per side, roughly 60–80 per plate. Terminal plate round, smooth approximately the size of three or four adjacent superomarginal plates.

Actinal surface with two complete plate series ( Fig. 21C ), each quadrate to polygonal in shape with four to six irregular plates distally adjacent to inferomarginal contact. Actinal plate covered by polygonal granules ( Fig. 21C, G ), 1 to 10 widely distributed over plate surface, most of these forming periphery around each plate. No pedicellariae observed.

Furrow spines five or six ( Fig. 21G ), more spines proximally in weakly convex to straight fan. Subambulacral granules, two to four, mostly three, pointed and conical in shape, set off from furrow spines by discrete space continuous across adambulacral plates. These pointed granules are about two to three times the size of the remaining granules on the plate. On one or two adambulacral plates per radius, one subambulacral granule, usually the one proximal to the mouth is replaced by a small tong-like pedicellaria, comprised of two elongate valves with smooth edges. Subambulacral granules sitting behind pointed granules, two to six, small and consistent in size with granules on actinal surface ( Fig. 21G ). Distalmost adambulacral plates with a single, large pointed subambulacral spine adjacent to furrow spines flanked by two smaller, blunt granules. Oral plates with 10 to 12 pointed, blunt spines with one enlarged blunt spine, projecting into mouth. These latter spines paired, so a total of two projecting into oral region. Oral plate proximal surface adjacent to oral convexity into mouth with a large, triangular spine (two total). Each half of the oral plate with six to eight, mostly seven paired, short spines along the edge of the contact between them.

In situ color of this species was a light orange with darker brick red-orange around periphery. Oral surface yellow to light orange ( Fig. 21F )

Material Examined. Holotype. USNM 1467573 Musician Seamounts , Papahanaumokea Marine National Monument, North Pacific Ocean. 31º51’N 162º54’W, 2352 m, Coll. M. Putts, NOAA Ship Okeanos Explorer EX 1708 , dive 8 (20170914/223327). 1 wet spec. R =2.0 r=0.9.

Images Examined

Forearc Seamount , Marianas region, 21.56671109, 145.518611, 3304 m EX1605 L3_IMG_20160629 T000640 Z_ ROVHD _ ASR _ SPO _ GAS _POL.jpg

Explorer Ridge (shallow), Marianas region. 20.72475133, 145.0613931, 1743 m EX1605 L3_IMG_20160702 T005539 Z_ ROVHD _ ASR _ GEO.jpg

Howland Island, Remote Pacific Islands region , 0.803422017, -176.6743123, 2333 m EX1703 _IMG_20170316 T220611 Z_ ROVHD.jpg

Howland Island, Remote Pacific Islands region , 0.80337905, -176.6743729, 2334 m EX1703 _IMG_20170316 T221212 Z_ ROVHD.jpg

Howland Island, Remote Pacific Islands region , 0.803407254, -176.6743383, 2334 m EX1703 _IMG_20170316 T221757 Z_ ROVHD.jpg

Beethoven Ridge, Musicians Seamount, 26.22286569, -159.1461377, 2509 m EX1708 _IMG_20170909 T203122 Z_ ROVHD.jpg

Musicians Seamount region , 27.8404838, -161.2924795, 2715 m EX1708 _IMG_20170912 T002030 Z_ ROVHD.jpg

purple variant

Beethoven Ridge, Musicians Seamount, 26.22296016, -159.1440676, 2390 m EX1708 _IMG_20170909 T225256 Z_ ROVHD.jpg

Feeding Observation

Johnston Atoll region, 15.09163377, -167.961119, 2539 m. EX1706 _IMG_20170728 T203756 Z_ ROVHD.jpg

SOLASTERIDAE

Figures

FIGURE 21. Okeanosaster hohonui n. gen, n. sp. Holotype USNM 1467573. A. Abactinal view. Scale bar=3.0 mm. B. Close-up of abactinal plates. Scale bar=1.0 mm. C. Actinal view. Scale bar=3.0 mm. D. Close-up of abactinal arm plates. Scale bar=1.0 mm. E. Lateral view showing marginal plates. Scale bar=2.0 mm. F. In situ observation from Forearc seamount, Marianas Islands, 3304 m. Scale bar=4.0 mm. G. Adambulacral armature including furrow and subambulacral spination. Scale bar=1.0 mm.