Echinasteridae Verrill, 1867

Kobayashi, Itaru & Fujita, Toshihiko, 2023, A New Shallow-water Species of the Genus Odontohenricia from Northern Japan (Asteroidea: Spinulosida: Echinasteridae), Species Diversity 28 (1), pp. 45-50 : 46-49

Family Echinasteridae Verrill, 1867

Genus Odontohenricia Rowe and Albertson, 1988 [New Japanese name: Nise-hime-hitode-zoku] Odontohenricia occasus n. sp. [New Japanese name: Yuyake-nise-hime-hitode] ( Figs 2 , 3A, B )

Material examined. Holotype. NSMT E-13876, Notsuka Cape , Rishiri Island , Hokkaido, Japan (45°14.0832′N, 141°16.3560′E), 3 m in depth, on 30 August 2021, fixed in 99.5% ethanol. One paratype. RTMECH4, Notsuka Cape, Rishiri Island, Hokkaido, Japan (45°13.9059′N, 141°16.7259′E), 3 m in depth, on 30 August 2021, fixed in 99.5% ethanol.

Diagnosis. Arms five. The abactinal skeleton is an irregular, open meshwork. Papular areas are larger than abactinal plates, containing 1 or 2 papulae. Abactinal spines are serrated at the tip. Abactinal spines, 1–10 gathered in a tuftlike pseudopaxilla that is widely separated from each other. Supero- and inferomarginal series are discernible. The intermarginal series extends to two-thirds of the arm length. Each adambulacral plate bears 6–14 subambulacral spines and 1 furrow spine. Each enlarged and unpaired oral spine has an opaque and serrated tip.

Description of holotype. Arms five, subcylindrical in shape, slender, and gradually tapering to the arm tip ( Fig. 2A ). R is 34.1 mm, r is 6.3 mm, and R/r ratio is 5.5r. The abactinal skeleton is an irregular open meshwork, constituted by many oval to rod-shaped, trilobate, and quadrilobate abactinal plates ( Fig. 2B ). Abactinal plates are partially imbricated with each other. Each abactinal papular area is larger than the surrounding plates, containing 1 or 2 papulae and often 1 secondary abactinal plate ( Fig. 2B, C ). Each abactinal plate bears 1–10 abactinal spines gathered in a tuft ( Fig. 2C ). Abactinal spines are arranged irregularly and grouped to form pseudopaxillae. Each pseudopaxilla is separated from its neighbors by relatively sunken papular areas or bared spaces and does not touch with other pseudopaxillae. A madreporite is located at the margin of the disk with several spines on its surface.

Abactinal spines are 0.39–0.45 mm in length. The spines are straight, cylindrical, and uniformly smooth, except for the tip with serration by splayed thorns ( Fig. 3A ).

Superomarginal plates are large quadrilobate or small rod-shaped and arranged in longitudinal series ( Fig. 2D ). These two forms are alternately arranged at the proximal half of the arms, and only large quadrilobate plates are continuously arranged at the distal half of the arms. Inferomarginal plates are quadrilobate and are arranged in longitudinal series. Supero- and inferomarginal plates are gradually decreasing in size toward the arm tips. Each quadrilobate superomarginal plate bears 9–11 spines, and each small rod-shaped superomarginal plate bears 1–4 spines. Each inferomarginal plate bears 10–19 spines. The supero- and inferomarginal spines are irregularly arranged in 2 irregular transverse rows ( Fig. 2E ). Beginning proximally, marginal series are separated from one another by up to two-thirds of the arm length. The superomarginal series gradually comes in contact with the inferomarginal series toward the arm tips ( Fig. 2D ). Intermarginal plates present, rod or quadrilobate in shape. These plates arranged irregularly at the proximal part of the arm but arranged in longitudinal series beyond the proximal one-third of the arm length. Papulae present along the marginal series ( Fig. 2E ).

Actinal plates are quadrilobate and arranged in 2 longitudinal series ( Fig. 2D, E ). The first series extends proximal half to two-thirds of the arm length. The second series is confined within one-third of the arm length. Each actinal plate bears 2–12 spines in 2 or 3 irregular rows ( Fig. 2E ). Papulae present between the inferomarginal and first actinal series, and the inferomarginal and second actinal series, but absent between the first and second actinal series, and the first actinal and adambulacral series.

Most adambulacral plates bear 1 furrow spines deep in the furrow and 6–14 subambulacral spines ( Fig. 2E, F ). Furrow spines and the adradial most subambulacral spine are arranged in a vertical row on the adradial surface of the adambulacral plate, and the remaining subambulacral spines are arranged in 2 or rarely 3 irregular transverse rows on the actinal surface of the adambulacral plate.

Each pair of oral plates, which forms a jaw, bears 1 large recurved and unpaired oral spine on its proximal edge ( Fig. 2G ). About proximal half or more of the spines are uniformly smooth without lateral serration, and the distal half or less of the spines is serrated with thorny projections ( Fig. 3B ). Each oral spine has numerous perforations on the overall length and lacks hyaline area.

The color in life is uniform reddish yellow on the abactinal side and more vivid yellow on the actinal side ( Fig. 2A ).

Variations in paratype. R is 35.5 mm, r is 6.3 mm, and R/r ratio is 5.6r. Superomarginal plates are more inconspicuous than the holotype, and the superomarginal plates in the arm base do not show any signs of regular series. Each inferomarginal, actinal, and adambulacral plate bears 9–17, 4–14, and 6–12 spines, respectively.

Distribution. Odontohenricia occasus n. sp. is only known from the type locality, Notsuka Cape, Rishiri Island, Hokkaido, 3 m in depth.

Etymology. The specific name “ occasus ” is a noun in apposition derived from the Latin word “ occasus ”, meaning “sunset”. The species depicts beautiful reddish yellow like sunset colors. The Japanese name “yuyake” also means sunset in Japanese, and “nise-hime-hitode” comes from the Japanese name of the congeneric species, O. hayashii ( Kogure 2018) . Therefore, the latter name is also designated for the Japanese name of the genus in this study.

Remarks. Among the species of Odontohenricia , three species, O. ahearnae , O. clarkae , and O. endeavouri share the long intermarginal series extending two-thirds of the arm length ( Rowe and Albertson 1988; O’Hara 1999; Clark and Jewett 2010) with O. occasus n. sp. However, the abactinal spines of the new species are 0.39–0.45 mm in length, while those of three congeners are 0.26 mm or less ( Rowe and Albertson 1988; Clark and Jewett 2010). Moreover, the morphology of the enlarged oral spines is different between the new species and the three species. O. occasus n. sp. has a serrated and opaque tip ( Fig. 3B ), whereas those of the three species have smooth or hyaline tip ( Rowe and Albertson 1988; Clark and Jewett 2010). The apically smooth and hyaline oral spines are also known from O. fisheri and O. hayashii ( Rowe and Albertson 1988; see Fig. 3D ). Additionally, we found a clear difference in the shape of abactinal spines observing three similarly sized NSMT specimens of Japanese species, O. hayashii (E-12592 from Tosa Bay, R = 40.1 mm, r = 6.0 mm; E-13878 from the Sea of Japan, R = 38.8 mm, r = 5.8 mm; E-13879 from the Sea of Japan, R = 35.1 mm, r = 5.1 mm). Each abactinal spine of holotype and paratype of O. occasus n. sp. has a large smooth surface without the lateral serration, which occupy more than basal two-thirds of the spines ( Fig. 3A ). In contrast, each abactinal spines of O. hayashii has a smaller smooth surface, which is limited to the basal half of the spines ( Fig. 3C ).

The genus Odontohenricia shows close morphological affinities with the confamilial genus Henricia Gray, 1840 except for the presence of enlarged and unpaired oral spines ( Rowe and Albertson 1988; O’Hara 1999). Of Japanese Henricia species, only H. pacifica Hayashi, 1940 has the long intermarginal series which extends two-thirds of the arm length, 10 or less abactinal spines, and 1 furrow spine and 10–15 subambulacral spines on each adambulacral plate like O. occasus n. sp. ( Hayashi 1940). However, the abactinal spines of H. pacifica are conical, not serrated, and sharply pointed ( Xiao et al. 2011), unlike those of the new species ( Fig. 3A ).

Figures

Fig. 2. Odontohenricia occasus n. sp., holotype, NSMT E-13876. A, Live specimen, abactinal (left) and actinal (right) views; B, denuded abactinal surface of the proximal portion of the arm; C, abactinal surface of the proximal portion of the arm; D, denuded lateral to actinal surface of the whole arm length; E, lateral to actinal surface at the proximal portion of the arm; F, distal view of 9th adambulacral plate, 8th and 9th adambulacral plates were excised from the arm; G, oral region, showing unpaired and enlarged oral spines (arrow heads). Abbreviations: ab, abactinal plates; ac1, first actinal series; ac2, second actinal series; ad, adambulacral series; f, furrow spine; im, inferomarginal series; pa, papulae; ps, pseudopaxillae; sm, superomarginal series; ss, subambulacral spines. Scale bars indicate 10mm for A, 1mm for B–G. Proximal is left in B–E.

Fig. 3. SEM images of spines of Odontohenricia occasus n. sp. and Odontohenricia hayashii. A, Abactinal spines of O. occasus n. sp., holotype, NSMT E-13876 (above), paratype, RTMECH4 (bellow); B, unpaired and enlarged oral spines of O. occasus n. sp., holotype, NSMT E-13876 (left), paratype, RTMECH4 (right); C, abactinal spines of O. hayashii, NSMT E-12592 (left four), NSMT E-13879 (right three); D, unpaired and enlarged oral spines of O. hayashii, NSMT E-13878 (left), NSMT E-12592 (center), and NSMT E-13879 (right, tip is partially broken), showing the hyaline area at the tip (arrow heads). Scale bar indicates 0.1mm in all images. Distal side is left in B and D.