Paragonaster stenostichus Fisher 1913

Kobayashi, Itaru, Sonoyama, Takayuki, Hibino, Mai, Kawano, Mitsuhisa & Kohtsuka, Hisanori, 2024, Pseudarchasteridae (Asteroidea: Paxillosida) in Japanese waters, with description of a new species and range extension of three species, Journal of Natural History 58 (25 - 28), pp. 949-964 : 956-958

publication ID	https://doi.org/ 10.1080/00222933.2024.2377336
DOI	https://doi.org/10.5281/zenodo.13758090
persistent identifier	https://treatment.plazi.org/id/03A3730A-8526-FFBE-FE07-CC4BFDEC3F97
treatment provided by	Plazi
scientific name	Paragonaster stenostichus Fisher 1913
status

Treatment

Paragonaster stenostichus Fisher 1913 View in CoL

[Japanese name: Minami-gokaku-hitode]

( Figure 3 View Figure 3 )

Paragonaster stenostichus ( Fisher 1913) View in CoL , p. 627; Fisher 1919: 232–235, pl. 60, fig. 2, pl. 70, fig. 2, pl. 71, fig. 1, pl. 91 figs. 10, 10a

Paragonaster ctenipes View in CoL – Oguro 1987: 46–51, figs. 1–2; Oguro 1990: 47

Material examined. OMNH-Iv 10662, 9 July 2020, north-west of Yamaguchi Prefecture, Sea of Japan, 34.9717°N, 130.8150°E, 130 m in depth, collected by the R / V Kaisei, fixed in 99% ethanol, R = 42.9 mm, r = 12.0 mm GoogleMaps .

Diagnosis. R/r> 3; most rectangular carinal abactinal plates as narrow as or narrower than length, except several first plates wider than length; lateral abactinal series extends to less than half of R; superomarginal plates widest in 3rd–4th plates; inferomarginal plates bear granules and 1–5 conical spines; actinal plates bear granules, spines and no pedicellariae; each adambulacral plate bears 6–7 furrow spines.

Description. Body stellate, flat ( Figure 3A View Figure 3 ). Arms five, broad proximally, gradually tapering to arm tips. R/r 3.6. Abactinal surface densely covered with numerous abactinal paxillae comprising abactinal plates and granules ( Figure 3B, C View Figure 3 ). Abactinal plates in two types, larger carinal and smaller lateral abactinal plates ( Figure 3C View Figure 3 ). Lateral abactinal plates mostly hexalobate, with cylindrical to prismatic paxillar columns, arranged in 5–6 regular longitudinal series on each side of arm. Paxillar columns wider than spaces between neighbouring paxillar columns. Adradial-most lateral abactinal series longest, extending to 29% of R. Carinal abactinal plates on proximal 30% of R, hexagonal with cylindrical paxillar columns and those on distal 70%, rectangular with prismatic paxillar columns. Carinal abactinal plates arranged in one regular longitudinal series extending to arm tip, wedged between two superomarginal series in distal 71% of R. Hexagonal carinal abactinal plates as narrow as length and gradually increase in width towards first rectangular plates. Rectangular carinal abactinal plates wider than length at first several plates but mostly narrower than length, gradually decreasing in width distally. Lateral and carinal abactinal plates bear mushroom-shaped granules without spines ( Figure 3B View Figure 3 ). Papular areas mostly contain one papula, every six surrounding one lateral abactinal plate ( Figure 3C View Figure 3 ). Madreporite single, round, convex, with radiated tortuous grooves, located at interradial disc.

Supero- and inferomarginal plates wide rectangular with oblong to oval ridges and arranged in longitudinal series along body margin ( Figure 3A, C–E View Figure 3 ). Superomarginal plates gradually increase in width up to 3rd–4th plates, and beyond these plates, gradually decrease in width distally ( Figure 3A, C View Figure 3 ). Inferomarginal plates gradually decrease in width distally ( Figure 3A, D View Figure 3 ). Supero- and inferomarginal series comprise 54 plates per interradius, without odd plates. Fascicular grooves narrow, shorter than ridges of neighbouring supero- and inferomarginal plates ( Figure 3C, D View Figure 3 ). Supero- and inferomarginal plates covered with mushroom-shaped granules and proximal to middle inferomarginal plates bear 1–5 conical spines arranged in one zigzag to two transverse series ( Figure 3E View Figure 3 ).

Actinal plates oval to rectangular, convex, and arranged in three longitudinal series ( Figure 3D View Figure 3 ). Actinal series confined within 26% of R. Each actinal plate bears mushroom-shaped to clavate granules and typically one major conical spine ( Figure 3E View Figure 3 ). Pedicellariae absent.

Adambulacral plates oval and arranged in one longitudinal series along the ambulacral furrow ( Figure 3D View Figure 3 ). Adambulacral series comprises 44 plates, extending to arm tips. Each adambulacral plate bears 6–7 furrow spines arranged in longitudinal curved series, one major subambulacral spine on plate centre and 12–15 minor subambulacral spines on plate margin ( Figure 3D, E View Figure 3 ).

Each pair of oral plates, forming jaw, bears one unpaired oral spine on its proximal edge ( Figure 3F View Figure 3 ). Each oral plate bears 25–28 oral spines arranged in three longitudinal series.

Tube feet biserial, with suckered discs.

Distribution. Waters adjacent to the Philippine Islands ( Fisher 1919); south and southeast off Shikoku Island, Japan ( Oguro 1987, 1990); north-west of Yamaguchi Prefecture, Sea of Japan (this study). Bathymetric range is 110– 314 m.

Remarks. The observed specimen aligns with the morphological characteristics of P. stenostichus described by Fisher (1913, 1919) (see Diagnosis and Key). Paragonaster ctenipes Sladen 1889 , reported by Oguro (1987, 1990) most probably belong to P. stenostichus , because most rectangular carinal abactinal plates are narrower than the length of his specimens, unlike those of P. ctenipes , which are wider than the length ( Sladen 1889; Fisher 1919). This is the first report of P. stenostichus from Japan, extending its northern distributional limit.