Paralophaster gomo Mah & Fujita 2020, n. sp.

Paralophaster gomo n. sp.

Figure 3 A–E

Etymology: Gomo is the Japanese word for “bristle” alluding to the highly spiny paxillae. Noun is held in apposition.

Diagnosis. A species with stellate body (R/r=3.0), thick disk, arms arched, acute interradial arcs. Abactinal paxillae bearing a tuft of 5 to 50, mostly 20–40 hyaline spines in linear, transverse series. Tufts round to oval in outline. Marginal plates comparable in size, morphology with abactinal plates, each with 20–50 spinelets, forming a distinct actinolateral border. Actinal region composed of flattened, wide adambulacral plates oriented transversely relative to tube foot groove and separated by tissue. Furrow spines, 10–15 in a curved fan.

Comments. Paralophaster gomo n. sp. differs sharply from the other known Paralophaster species in the possession of 20–40 (up to 50) glassy spinelets on abactinal and marginal paxillae and having 10 to 15 furrow spines and seven to nine subambulacral spines. Paralophaster hyalinus displays only 16–23 paxillar spinelets with three or four furrow spines and four or five subambulacral spines. A survey of the Antarctic Paralophaster spp. (A. M. Clark 1962) shows a comparable number of paxillar spinelets (30–40), but far fewer furrow spines (two or three) in P. antarcticus (Koehler 1912) with far fewer paxillar spinelets and furrow spines in P. godfroyi (Koehler 1912).

Occurrence. Japan, Ogasawara Islands, Izu Islands, 133–211 m.

Description. Body stellate (R/r=3.0), disk thick, strongly arched, arms round and trunk-like, oral surface flat. Interradial arcs acute (Fig. 3A).

Abactinal skeleton reticulate but close-set, central regions with primarily single but a minority with two to four papular pores emerging through a translucent membrane framed by the skeletal bars (Fig. 3B). Papular regions largest proximally on disk becoming smaller distally along arms to such an extent that papular areas adjacent to arm terminus are tightly compressed and/or absent. In NMST E-11260 (R=1.2), skin is translucent proximally becoming opaque distally. Intersection of skeletal plates around papular pores with thick tufts of webbed, hyaline spinelets, approximately five to 50, mostly 20–40, per tuft. Each hyaline, serrated spinelet with one or two tips. These paxillar tufts occur in ordered, linear series along the arms. In larger individuals (R>2.0) these tufts are densely packed but are more widely spread out in smaller individuals (R=1.2). Tufts are round to oval-shaped in outline. Paxillar tufts are largest on the primary circlet and those of the subsequent six to 10 carinal plates are very prominent, showing greater size disparity between these and the other plates observed on the smallest specimen (R=1.2) (Fig. 3E). Larger specimens show more homogeneity between carinal and primary papillae tuft size and shape. Interradial disk regions with distinct folded area between arms. Madreporite strongly convex. No pedicellariae observed.

Superomarginals, 32–54 per interradius (16–17 per arm), significantly smaller than inferomarginals, comparable to identical in size and morphology with abactinal plates. Inferomarginal plates, approximately 32 to 36 per interradius, much larger, at least three to five times larger than superomarginal, covered by webbed, serrated spinelets, 20–50 and forming distinct actinolateral border. The smaller individual, NMST E-11260, shows three larger primary spines with serrated edges. Both marginal plate series show widely distinct spacing (Fig. 3E).

Actinal region composed of wide, flattened, adambulacral plates, arranged transversely relative to tube foot groove, separated by distinct tissue filled gap (Fig. 3D). Adambulacral plates and gaps in direct contact with inferomarginal series with approximately two adambulacral plates corresponding to every inferomarginal plate. The side of the adambulacral extending into the tube foot groove with a curved fan of webbed hyaline furrow spines, 10 to 15. A second series of spines (subambulacrals) in a curved, nearly transverse fan sits a significant difference away from the furrow spines at an oblique angle. The spines on the second series, seven to nine in number and approximately twice as thick as those on the furrow spines. Oral plates with smooth, bare surface, strongly convex paired plates adjacent to oral region, crest formed by these plates each bearing tuft of 10 to 20 hyaline spinelets. Oral plate furrow spines, 15 to 20 pointed and glassine in texture.

Material Examined. Holotype. NSMT E-11294, Tosa Bay, Japan, 33˚14.993′N, 133˚36.523′E–33˚14.647′N, 133˚36.215′E, 151–155 m, Coll. R / V Kotaka-maru, 14 May 1997, 1 wet spec., R =2.4 r=1.0. Paratypes. NMST E-11260, West of Amami-Oshima Island, Kagoshima Prefecture, Japan, 28˚21.23′N, 129˚13.60′E–28˚21.41′N, 129˚14.10′E, 285–288 m, Coll. R / V Toyoshio-maru, St. 7 1 wet spec., R =1.2 r=0.4; NSMT E-11295, Tosa Bay, 33˚14.993′N, 133˚36.523′E–33˚14.647′N, 133˚36.215′E, 151–155 m, Coll. R / V Kotaka-maru, St. 15, 14 May 1997, 1 wet spec., R =2.4 r=1.0; NSMT E-7119, Between Hachijyo-jima Island and Mikura-jima Island, Izu Islands, 33˚27.3′N, 139˚42.6′E–33˚27.7′N, 139˚42.4′E, 200–211 m, Coll. R / V Shin’yo-maru, St. 20, 21 October 2003, 1 wet spec., R =1.2 R =0.3; NSMT E-10641, South west of Chichi-jima Island, Ogasawara Islands., 27˚1.536′N, 142˚7.388′E–27˚1.855′N, 142˚7.414′E, 133–134 m, Coll. R / V Koyo, St. KY-16-01, 11 July 2015, 1 wet spec., R =8.0 r=3.0.