Churaumiastra hoshi, Mah & Kogure & Fujita & Higashiji, 2024

Mah, Christopher L., Kogure, Yoichi, Fujita, Toshihiko & Higashiji, Takuo, 2024, New Taxa and Occurrences of Mesophotic and Deep-sea Goniasteridae (Valvatida, Asteroidea) from Okinawa and adjacent regions, Zootaxa 5403 (1), pp. 1-41 : 4-8

Churaumiastra hoshi nov. gen. nov. sp.

Japanese name: Churaumi-gokaku-hitode

Churaumi: beautiful sea, gokaku: pentagonal, hitode: seastar

FIGURE 1A–F , 2A–D

Etymology

The genus for this species is named for Churaumi of the Churaumi Okinawa Aquarium, which translates to “beautiful sea” in English and “- astra ”, the feminine gender for star. The species epithet hoshi is the Japanese word for star, alluding to this species strikingly stellate appearance. Species name is held in apposition.

Diagnosis

Body planar, strongly stellate (R/r=2.3), arms elongate, interradial arcs weakly curved. Body covered by a dense cover of granules which forms a pavement like covering over the abactinal, marginal, and actinal surfaces.Abactinal plates hexagonal, disk only with no abactinal plates on arms. Superomarginals directly abutted over mid radius along arm distance ( Fig. 1A ). Superomarginal plates form distinct frame around disk, comprising approximately 20% of the total “r” distance ( Fig. 1A–B ). Actinal regions large with 4 to 6 distinct series in chevron formation. Individual actinal plates quadrate ( Fig. 1C ). Furrow spines four, blunt, quadrate in cross section ( Fig. 1F ). Subambulacrals in approximately 3 irregular series with series adjacent to actinal plates, irregularly transitioning in size with actinal granules. Adambulacral spines, blunt, flattened and nearly flush with actinal surface ( Fig. 1E–F ).

Taxonomic Comments

Churaumiastra hoshi n. gen. n. sp. possesses an unusual set of adambulacral spination that is flattened to such an extent that they are flush with the actinal surface ( Fig. 1E–F ). Only two other goniasterid species have comparable adambulacral morphology; Glyphodiscus magnificus Mah 2005 and Iconaster longimanus (Möbius, 1859) .

A further distinctive character in Churaumiastra is the tightly arranged granules that form a smooth, almost featureless pavement over the abactinal, marginal and actinal surfaces, a similar surface is also observed in the shallow water west Indian Ocean goniasterid Monachaster sanderi . Although Iconaster and Glyphodiscus completely lack surface granulation, they possess comparably smooth abactinal, marginal and actinal surfaces.

Churaumiastra , Iconaster and Glyphodiscus all possess superomarginals which abut over the radius of each arm and possess a comparably similar planar body form with elongate, triangular arms. Blake (1983, 1990) argued that characters such as these might be part of a morphology serving to defend soft tissue against predators. In contrast to goniasterids with more elongate and more widely spaced furrow spines (e.g., Pentagonaster ), the relatively short and thickened furrow spines in these genera do not appear to permit the interlacing between furrow spines as the furrow closes. However, the ambulacral furrow in these genera does tend to be very narrow and fairly rigid by comparison, suggesting ease of immediate closure.

Two other goniasterid genera, Lithosoma and Pontioceramus display similar planar body form, abutted arm superomarginals and smooth but closely arranged granules around the plate periphery, suggesting these two genera also display affinities with Churaumiastra , Iconaster and Glyphodiscus , perhaps as part of a larger grouping within the Goniasteridae .

Ecological Comments

The Okinawan specimen was observed on what appeared to be a coarse, rocky substrate adjacent to what appeared to be an octocoral ( Fig. 2A ). Many goniasterids feed on octocorals (e.g. Mah 2020), a potential prey item for this species. The Ashmore Reef specimen was similarly observed on sponges, a possible prey, on a loosely consolidated coarse, pebbly substratum.

Occurrence

Okinawa, Japan, 247 m.

Outside Japan. the Philippines, Indian Ocean. Ashmore Reef, Western Australia, 100– 200 m.

Description

Body flattened planar, strongly stellate (R/r=2.37–2.6). Arms triangular, interradial angles with broad, obtuse curves.

Abactinal surface planar, fasciolar grooves absent. Abactinal plates flattened, hexagonal arranged in distinctive series closely abutted, plates angular, identical in overall shape. Radial plates in regular, radial series, becoming more irregular interradially. Plates larger proximally on disk, but smaller distally adjacent, wider in shape, in contact with superomarginals. Abactinal plates only on disk, absent from arms. Plates covered by dense cover of angular granules, each quadrate to polygonal in outline forming an almost solid mosaic. Individual plates with 40–80 granules per plate with 20–30 granules forming periphery. Granules on radial regions, enlarged,(approximately 2x the size of central granules), forming more distinctive radial borders than those interradially. Granules, mostly three, polygonal to round, present over each papula slightly enlarged relative to other granules on radial regions. Granules interradially not enlarged, peripheral layer indistinct from central granules. Papulae absent interradially. Granules largely contiguous with those on marginal plates. Superomarginal plates form prominent frame around disk, forming 20% of total “r” distance (center of disk to disk edge). Madreporite flattened, triangular in outline, with well-developed sulci, flanked by three abactinal plates. Granules, four to 14, enlarged relative to other abactinal granules, in contact with each side. Anus covered by five large, quadrate, angular granules.

Marginal plates, 28–30 from armtip to armtip. Superomarginals and inferomarginals mostly with 1:1 correspondence but with minor offset distally. Distalmost superomarginals, nine to 11, abutted along midline. Distalmost superomarginals slightly offset. Marginal plates quadrate but rounded in outline with a dorsolateral edge. rounded. Granules, 400–700, angular, quadrate to irregular in shape, densely articulated on superomarginal and inferomarginal plates forming smooth mosaic. Distalmost four to six superomarginals with large quadrate to round, smooth bare spot on abactinal surface. Inferomarginals also completely covered by densely packed, angular granules. Granules on marginal plates flattened and form flush surface contiguous with abactinal surface on disk. Distalmost inferomarginals, two to four with prominent single tubercle.

Actinal plates composed of four to six chevrons. Plates, quadrate in distinct series adjacent to adambulacrals, becoming smaller, more irregular in shape and arrangement adjacent to inferomarginal contact. Actinal surface covered by densely arranged granules, 14–60 per plate. All actinal granules form flush continuous surface. Each granule quadrate to irregularly polygonal, all contiguous with inferomarginal granules and flush with adambulacral granules and accessories such that actinal surface appears smooth. Boundaries between granules not apparent on some. Overall appearance of granular covering identical to those on abactinal and inferomarginal covering.

All furrow spination and accessories flush and level with actinal granulation. Furrow spines, four (on most adambulacrals) and six(first two proximal adambulacrals).Spines are quadrate in cross-section, thick, angular.Furrow spines backed by three to seven series of close-fitting subambulacral granules, flattened, angular. Subambulacrals enlarged, three immediately behind first two series of furrow spines, becoming smaller more numerous, contiguous with actinal granulation. Mouth plates with furrow spines six, similar in appearance to those on other adambulacrals, flanked by enlarged subambulacrals, four immediately behind. Oral plates covered by angular, irregularly shaped granules 15–25, some of which pair off across the gap dividing the paired oral plates.

In situ color on the abactinal surface varied between Pacific and Indian Ocean specimens, although the pattern itself was consistent. The Japanese specimen ( Fig. 2A ) abactinal surface displayed yellow triangular areas on the proximal arm regions with a white central disk, interradii and distal arm section. The Indian Ocean Ashmore Reef specimen was orange where the Pacific Japanese specimen was yellow and yellow where the Pacific specimen was white. ( Fig. 2B ). The actinal surface of the Ashmore reef specimen was a solid tan to dull white.

Material Examined

Holotype. NSMT E-14497 off Onna village located in the mid-western part of Okinawa Island, the depression of rock of under-water reef called Onna-sone, 26°34.0619 N, 127°48.3038 E; 247 m; 24 March 2021, 1 wet spec. R=6.3 r=2.5.

Additional non-type specimens from the Okinawa region are currently kept on display at the aquarium. R= 61 mm, r = 22 mm, R/r = 2.8, R = 56 mm, r = 21 mm, R/r = 2.7, R = 60 mm, r = 23 mm, R/r = 2.6.

Paratypes. PNM 6914 ( Philippines). Balut Island, Mindanao , Philippines. 100–200 m. 1 dry spec. R=6.3 r=2.4.

USNM 1110197 . Aliguay Island , Mindanao , Zamboanga del Norte, Philippines. 200 m. 1 dry spec. R=5.61, r= 2.37 cm.

CASIZ 185656 . Balut Island, Mindanao , Philippines, about 200m. 1 dry spec. R=5.2 r=2.1.

CASIZ 185657 . Balut Island, Mindanao , Philippines, about 200m. 1 dry spec. R=3.8 r=1.3.

WAM Z97558 Ashmore Reef, Western Australia , 12.32001331’ S 123.09032385 E, 171 m, Coll. N.G. Wilson, C.S. Whisson, Coll. 11 April 2021. R=5.6 r=2.2

Figures

FIGURE 1. Churamiastra hoshi n. gen. sp. Paratype USNM 1110197, A. Abactinal view. A.1. (inset) Abactinal plate surface. A.2. (inset) Madreporite and abactinal plate surface detail. B. Abactinal and adjacent superomarginal plate surfaces. C. Actinal view. D. Lateral view showing superomarginal and inferomarginal plate surfaces. E. Contact between actinal intermediate plates and inferomarginal plate series. F. Oral region on actinal surface. Scale bars: A, C=10.0 mm, A.1–A.2 =2.0 mm, B=5.0 mm, D–E=3.0 mm, F=2.0 mm.

FIGURE 2. Churamiastra hoshi n. gen. sp. In situ observations. A. Okinawan specimen. B. Ashmore reef specimen (Australia). WAM Z97558 (for B–D) C. Abactinal surface. Deck photo. showing live coloration. D. Actinal surface.