Disasterina akajimaensis, Saba & Iwao & Fujita, 2012

Saba, Masaki, Iwao, Kenji & Fujita, Toshihiko, 2012, A New Asterinid Sea Star, Disasterina akajimaensis (Echinodermata: Asteroidea) from the Ryukyu Islands, Japan, with Notes on the Genus Disasterina, Species Diversity 17 (1), pp. 21-28 : 24-27

Disasterina akajimaensis sp. nov.

[New Japanese name: Akajima-numeri-itomaki-hitode]

( Table 1 ; Figs 2–6)

Disasterina odontacantha : Saba et al. 2008: 19–20. [Not Disasterina odontacantha Liao, 1980 ]

Material examined. H olotype: NSMT E-6758 , Kushibaru beach, Akajima Island, Ryukyu Islands (26°12.6'N, 127°16.6'E), intertidal, under rock, collected by M. Saba, on 19 November 2006. The specimen was directly preserved in 99% ethanol .

Description of holotype.B ody thin, stellate with 5 tapering arms, slightly convex abactinally, at actinally (Fig. 2). R/r=16.9/ 8.1 mm =2.1. Body entirely covered by smooth integment obscuring underlying skeletal plates in life, but plates visible a er preservation in alcohol.

Abactinal plates imbricated, irregular in shape (circular, triangular, oval, and slender), and variable in size, maximally 1.6× 0.4 mm; unarmed, except 4 plates surrounding anal pore each having 2–5 short, sacciform spinelets (Figs 3A–C, 4A). Ten large and slender and about 25 small abactinal plates almost regularly arranged to surround pentagonal area at center of disc (Fig. 3A). In central pentagonal area, about 43 small abactinal plates arranged in mesh with papulae in spaces. Outside central pentagonal area, abactinal plates in interradial triangular part strongly imbricated (Fig. 3A); 10–12 large plates attached rmly to each other to form rigid area (Fig. 3A) internally connected with internal pillar (Fig. 5A). Abactinal plates in radial part contiguous or slightly imbricated, arranged irregularly in mesh with papulae in openings (Fig. 3A, C). Those just inside marginal plates strongly imbricated, smaller than those in inner part (Fig. 3C). Anal pore present at center of disc enclosed by above-mentioned plates with spinelets (Fig. 3A). Madreporite roundish pentagonal, situated just outside central pentagonal area, with about 16 sacciform spinelets on periphery (Fig. 3B).

Superomarginal plates minute, 5–7 in number, not forming distinct series. Inferomarginal plates 30–35 in number, arranged in series; spatulate, each bearing transverse distal fringe of 3 (rarely 2 or 4) webbed sacciform spinelets (Fig. 3F). Terminal plates roundish rectangular.

Papulae large, isolated, and present only on abactinal surface; numerous (42 in number) in central pentagonal area, sparse in radial part of ray (Fig. 3C).

On actinal surface, interradial uncalci ed area present just distal to oral plate pair, covered with thin membrane in which 3 small, thin plates embedded (Figs 3D, 6).

Each oral plate bearing 4–5 oral spines; lacking suboral spines (Figs 3D, E, 6). Oral spines arranged closely in curved line; webbed basally by thin membrane; inner 3 spines longer than outer 1 or 2.

Adambulacral plates 33–35 in number, each with 3 (rarely 1 or 2) glassy furrow spines webbed by thin membrane, and 1 long, glassy subambulacral spine (Figs 3E, 6). Actinolateral plates roughly arranged in longitudinal rows; those of innermost two rows larger, each bearing long, sacciform actinolateral spine and innermost one extending just before terminal plate; outer rows unarmed, strongly imbricated (Fig. 3E). Most of oral spines, furrow and subambulacral spines, and actinolateral spines with 1–3 small transparent terminal teeth (Fig. 4B).

Superambulacral plates present irregularly, very small (Fig. 5C). Superactinal plates consisting of a single plate, present at internal margin, numerous interradially, becoming fewer distally (Fig. 5B).

Color in life uniformly light brown abactinally, whitish actinally (Fig. 2).

Remarks.Thi s specimen was recorded as a young form of D. odontacantha in our preliminary report ( Saba et al. 2008). The present new species is closely related to D. odontacantha as well as D. abnormalis , both of which share low and at arms without a median keel, and a conspicuous interradial uncalci ed area. It is closer to D. odontacantha but distinguishable by the absence of spinelets on most abactinal plates in contrast to the presence of the 1–2 spinelets, and by the 4 or 5 closely placed oral spines without any gap between them, in contrast to 3 or 4 more widely spaced spines. It is also distinguishable from D. abnormalis by the absence of a suboral spine on each oral plate in contrast to the presence of a long, sacciform one. The di erences from the other species are shown in Table 1 .

This is the rst report of this genus from Japanese waters.

Distribution.On ly from the type locality, Akajima, the Ryukyu Islands, Japan (present study).

Etymology.Th e speci c epithet akajimaensis is derived from the island of Akajima, where the holotype was collected. New Japanese names given for this genus and species are Numeri-itomaki-hitode-zoku and Akajima-numeriitomaki-hitode, respectively. Akajima is the locality, while in Japanese “numeri” refers to the slimy nature of the body surface, an “itomaki” is a spool used in sewing with a shape that looks like asterinid sea stars, “hitode” are seastars, and “zoku” means genus.