Paragonaster hoeimaruae Kobayashi, Sonoyama, Hibino, Kawano & Kohtsuka, 2024, sp. n.
Creators: name: Kobayashi, Itaru
name: Sonoyama, Takayuki
name: Hibino, Mai
name: Kawano, Mitsuhisa
name: Kohtsuka, Hisanori
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Asteroidea
Paxillosida
Pseudarchasteridae
Paragonaster
Paragonaster hoeimaruae

description: Paragonaster hoeimaruae sp. n.
[New Japanese name: Hoei-miyabi-momiji-hitode]
(Figure 4)
http://www.zoobank.org/urn:lsid:zoobank.org:pub:75CBAFBA-369A-4E28-A5A9-
F4F3A541516F
Material examined. Holotype: OMNH-Iv 10664, 18 December 2023, off Itou, Sagami Sea, Japan, 34.6934°N, 139.0663°E, 350 m in depth, collected by the fishing boat Hoei-maru, fixed in 99% ethanol, R = 54.5 mm, r = 21.9 mm. Paratype: OMNH-Iv 10663, 19 July 2021, north of Yamaguchi Prefecture, Sea of Japan, 35.4983°N, 131.5700°E, 150 m in depth, collected by the R / V Kaisei, fixed in 99% ethanol, R = 67.4 mm, r = 28.3 mm.
Diagnosis. R/r 2.4–2.5; most rectangular carinal plates wider than length; lateral abactinal series extends to less than one-half of R; superomarginal plates widest in 4th–7th plates; inferomarginal plates bear granules and 1–5 leaf-shaped spines; actinal plates bear granules, spines and pedicellariae; each adambulacral plate bears 5–7 furrow spines.
Description of holotype. Body stellate, flat (Figure 4A). Arms five, broad proximally, gradually tapering to arm tips. R/r 2.5. Abactinal surface densely covered with numerous abactinal paxillae, comprising abactinal plates, granules and spines. Abactinal plates in two types: larger carinal and smaller lateral. Lateral abactinal plates mostly hexalobate, with tabulate paxillar columns, arranged in 7–8 regular longitudinal series on each side of arm (Figure 4A, B). Paxillar columns narrower than spaces between neighbouring paxillar columns. Adradial-most lateral abactinal series longest, extending to proximal 44% of R. Carinal abactinal plates on proximal 40% of R, hexagonal with tabulate paxillar columns and those on distal 60%, 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 56% of R. Hexagonal carinal abactinal plates as narrow as or narrower than length and gradually increase in width towards first rectangular plates. Most rectangular carinal abactinal plates wider than length and gradually decrease in width distally. Lateral and carinal abactinal plates bear mushroom-shaped granules and conical spines on centre and margin of paxillar columns, respectively (Figure 4C). Papular areas mostly contain one papula, every six surrounding one lateral abactinal plate. Madreporite single, round, convex, with radiated tortuous grooves, located at interradial disc (Figure 4A). Anus at disc centre (Figure 4D).
Supero- and inferomarginal plates wide rectangular with oblong to oval ridges and arranged in longitudinal series along body margin (Figure 4A, B, E, F). Superomarginal series gradually increase in width up to 4th–7th plates, and beyond these plates gradually decrease in width distally (Figure 4A). Inferomarginal plates gradually decrease in width distally. Supero- and inferomarginal series comprise 46 and 48 plates per interradius, without odd plates, respectively. Fascicular grooves narrow, shorter than ridges of neighbouring supero- and inferomarginal plates (Figure 4B, E). Supero- and inferomarginal plates covered with mushroom-shaped to clavate granules and proximal inferomarginal plates bear 1–5 leaf-shaped spines arranged in one or two transverse series (Figure 4F).
Actinal plates oval, triangular, rhomboid, convex (Figure 4E). Most actinal plates arranged irregularly, but rhomboid actinal plates arranged in one regular longitudinal series along adambulacral series. Actinal series comprises 11 plates, extending to 43% of R. Each actinal plate bears mushroom-shaped to clavate granules and several plates bear one major leaf-shaped spine (Figure 4F). Most plates in actinal series also bear transverse series of 4–9 leaf-shaped spines on their margins, forming fasciculate pedicellariae facing with series of spines on adjacent actinal plates (Figure 4F, G). Fasciculate pedicellariae 6–9 in each actinal interradius.
Adambulacral plates rhomboid and arranged in one longitudinal series along ambulacral furrow. Adambulacral series comprises 37 plates, extending to arm tips. Each adambulacral plate bears 5–7 furrow spines arranged in longitudinal curved series and 9–17 subambulacral spines arranged irregularly (Figure 4F).
Each pair of jaw-forming oral plates bears one unpaired oral spine on its proximal edge (Figure 4H). Each oral plate bears 20–21 oral spines arranged in two longitudinal series.
Tube feet biserial with suckered discs (Figure 4A, F).Body colour uniform red on abactinal side, beige on actinal side (Figure 4A).
Variations in paratype. Adradial-most lateral abactinal series extends to 46% of R. Carinal abactinal series wedged between two superomarginal series in distal 54% of R. Superomarginal series comprises 24 plates, gradually increasing width up to 5–6th plates and beyond these plates, gradually decreasing width distally. Inferomarginal series comprises 25 plates. Proximal inferomarginal plates bear 1–3 leaf-shaped spines. Actinal series along adambulacral series comprise 13 plates, extending to 35% of R. Each actinal plate lacks leaf-shaped major spines. Fasciculate pedicellariae only on proximal actinal plates, 5–9 in each actinal interradius. Each oral plate bears 23–24 oral spines arranged in two longitudinal series.
Distribution. Paragonaster hoeimaruae sp. n. is only recorded from Japanese waters: south-east of Izu Peninsula, Sagami Sea; north-west of Yamaguchi Prefecture, Sea of Japan. Bathymetric range is 150– 350 m.
Etymology. The specific epithet ‘ hoeimaruae ’ and the Japanese name ‘hoei’ are derived from the fishing vessel Hoei-maru which collected the holotype specimen, and ‘miyabimomiji-hitode’ follows the Japanese name of the genus proposed in this study.
Remarks. Of the eight living and three fossil species of the genus, P. hoeimaruae sp. n. is most closely related to two north-west Pacific species (P. chinensis Liao, 1983 and P. obtusus) and one Atlantic species (P. grandis H.L. Clark 1941) by sharing the short arms with an R/r <3 (Alcock 1893; Fisher 1919; Halpern 1972; Hayashi 1973a, 1973b; McKnight 1973; Liao 1983; Blake and Aronson 1998; Clark and Downey 1992; Jagt et al. 2014; Stevens 2020). However, this new species is readily distinguished from the three short-arm species in having fasciculate pedicellariae on actinal plates (Figure 4F). Moreover, P. hoeimaruae is distinguished from the three congeners in having lateral abactinal series extending to less than one-half of R (Figure 4A) [vs more than one-half of R in P. chinensis and P. obtusus (Hayashi 1973a, 1973b; Liao 1983)], most rectangular carinal abactinal plates are wider than length (Figure 4B) [vs narrower than length in P. obtusus (Figure 2B)], superomarginal plates that are the widest in 5–7th plates (Figure 4A) [vs widest interradially in P. grandis and P. obtusus (Halpern 1972; Hayashi 1973a, 1973b; Figure 2A, B)], inferomarginal plates covered with granules with a few spines (Figure 4F) [vs completely covered with spines without granules in P. grandis (Halpern 1972)] and adambulacral plates bearing 5–7 furrow spines [vs 8–10 furrow spines in P. grandis (Halpern 1972)].
A KEY TO LIVING SPECIES OF THE GENUS PARAGONASTER
A key is provided based on our observations and other descriptive publications (Sladen 1889; Alcock 1893; Perrier 1894; Fisher 1919; Halpern 1972; Hayashi 1973a, 1973b; McKnight 1973; Liao 1983).
1. Proximal carinal plates wedged between two superomarginals are as narrow as or narrower than length ...................................................................................................................... 2
– Proximal carinal plates wedged between two superomarginals are wider than length ............................................................................................................................................. 6
2. Actinal plates bear spines .............................................................................................................. 3
– Actinal plates lack spines; Indo-West Pacific Ocean .................. .................. P. tenuiradiis
3. Superomarginal plates gradually increase in width up to 6th–7th plates, beyond which width gradually decreases distally ................................................................................ 4
– Interradial superomarginals are the widest, decreasing in width distally .................. 5
4. Carinal abactinal plates increase slightly in width up to the first plate wedged between two superomarginal plates; beyond this plate, they gradually decrease in width distally; inferomarginal spines 1–5 on each proximal plate; Indo-West Pacific .................................................................................................................................. P. stenostichus
– Carinal abactinal plates gradually decrease in width distally; inferomarginal spines 8–15 on each proximal plate; South Pacific Ocean .................... .................... P. ridgwayi
5. R/r> 4.0; lateral abactinal series extends to less than one-third of R; Atlantic Ocean .................................................................................................................................................... P. subtilis
– R/r <2.5; lateral abactinal series extends to more than one-half of R; north-west Pacific Ocean ...................................................................................................................... P. obtusus
6. Interradial superomarginals are the widest, decreasing in width distally; inferomarginal and actinal plates are covered with spines without granules; each adambulacral plate bears 8–10 furrow spines; Atlantic Ocean .......................................... P. grandis
– Superomarginal plates gradually increase in width up to 4–7th plates, beyond which width gradually decreases distally; inferomarginal and actinal plates are covered with granules with or without spines; each adambulacral plate bears <8 furrow spines; Pacific Ocean ........................................................................................................................................ 7
7. R/r> 3.0; each adambulacral plate bears one major subambulacral spine two or more times longer than the others; Indo-West Pacific Ocean .......... .......... P. ctenipes
– R/r <3.0; adambulacral plate bears no major subambulacral spines; north-west Pacific Ocean ....................................................................................................................................... 8
8. Lateral abactinal series extends to more than one-half of R; pedicellariae are absent ................................................................................................................................................ P. chinensis
– Lateral abactinal series extends to less than one-half of R; pedicellariae are present... P ................................................................................................................... hoeimaruae new species
description: Published as part of 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, pp. 949-964 in Journal of Natural History 58 (25 - 28) on pages 958-962, DOI: 10.1080/00222933.2024.2377336, http://zenodo.org/record/13758076