Hyalinothrix vitrispinum, Mah & Fujita, 2020

Mah, Christopher L. & Fujita, Toshihiko, 2020, New species and occurrence records of Japanese Solasteridae and Ganeriidae including a new species of Paralophaster from the North Pacific with an overview of Hyalinothrix, Zootaxa 4750 (1), pp. 67-100 : 90-93

Hyalinothrix vitrispinum n. sp.

Figure 9 A–D

Etymology: The species epithet is derived from the Latin vitrum for glass or glassy and spinum for spine alluding to the elongate, glassine spines present in this species.

Diagnosis. A species diagnosed by the elongate glassy spinelets present on the paxillar surface, which extend to the surface of adjacent paxillae. Furrow spines six or seven.

Comments. This species shares the most distinguishing characters with Hyalinothrix millespina , primarily the elongate glassine spinelets present on the abactinal and surface paxillae which extend well beyond the surface of each plate, forming an interlocking array of spinelets between the plates above the papulae and the fasciolar grooves. Subambulacral spines glassine forming thick, dense tufts proximally.

This species is distinguished by the presence of six or seven furrow spines and elongate glassy spinelets on the surface paxillae, numbering mostly between 30 to 40, but exceptionally up to 60.

Occurrence: Balut Island, Philippines, 150– 250 m.

Description. Body strongly stellate (R/r=6.6–7.0), arms wide at base, tapering distally. Arms cylindrical in cross-section ( Fig. 9A ).

Abactinal plates paxillate, plates low to moderately height, forming well-defined fasicolar grooves. Plate bases flattened, lobate in shape, mostly four but some three-lobed. All have with overlapping, imbricating bases. Approximately four plates with lobes forming corners around each papular pore. Tissue covers overlapping basal plates. Each plate widening at top forming wide, broader plate surface than base; abactinal plate surface round to polygonal in outline, abactinal plate surface convex, covered with spines. Lateral edge of each plate covered by 20–60, mostly 30–40 fine, elongate glassine spines ( Fig. 9B ) with single or two-pronged tips forming an overlapping canopy over the fasciolar groove below it. Central plate surface covered by 20–40 shorter hyaline spines similar to those around the plate edges, widely spaced. Central surface of most plates on the holotype show signs of erosion; spination absent. Abactinal plates homogenous in shape, with more polygonal to oval shaped plates occurring proximally and rounder plates occurring more distally. Plates larger proximally becoming smaller distally. Radial series are irregular, carinal series indistinct but lateral arm plates form distinct transverse series along the adradial to lateral arm surfaces. Madreporite strongly convex with distinct sulci, but obscured by glassine spines forming canopy on adjacent paxillar plates. No pedicellariae.

Marginal plates, approximately 120–130 per interradius (at R=5.4) versus 45–50 at R=3.5, individual plates indistinct from those on abactinal surface with identical spine types and numbers. Recognition of marginals follows positional criterion of Blake (1976) and were tracked from the terminal plate, alongside the adambulacrals along the arms, then interradially.

Actinal plates present in two series in weakly chevron-like pattern, restricted to disk with none extending along the arm ( Fig. 9D ). Actinal paxillae are continuous in series with those on abactinal and lateral surface, identical in appearance with consistent numbers of glassine abactinal spines.

Furrow spines blunt, six or seven, mostly six, per plate in weakly palmate series with smallest spines at ends and tallest spines present centrally on fan ( Fig. 9D ). Furrow spines five in six-armed paratype (CASIZ 229110). Smallest spines are at least <25% of the length of longest spines. Furrow spines most numerous proximally decreasing distally. Furrow spines set off from large subambulacral spine tuft, approximately 20 to 50 densely packed glassine spinelets displaying single or two-pronged tips similar to those on the abactinal paxillar plates. Subambulacral spines most elongate adjacent to the furrow spine with shorter spines more similar to actinal spines on the actinal side of the adambulacral plate. Mouth plates with six to eight furrow spines, and a large, dense, spiny tuft identical to the subambulacral tufts on the adambulacrals, obscuring the oral region.

A single six armed individual of this species corresponds in nearly every character, except that furrow spines number five on each adambulacral plate rather than six or seven, as in the holotype and paratype. This specimen is slightly larger (R=4.1) than the second paratype (3.5), suggesting factors other than growth are associated with the variation in furrow spine number.

Another paratype, PH 06s displays a bifurcated arm tip with two 2.0 cm tips branching from a fork on the distal arm end, including two complete ambulacral furrows split from the bifurcation point.

Material Examined. Holotype: NMEC 6916 , Balut Island , Philippines, 150–250 m, 1 dry spec., R =5.4 r=0.8.

Paratypes: CASIZ 229109 , Balut Island , Philippines, 150–250 m, 1 dry spec ., R =3.5 r=0.5. CASIZ 185670 , Aliguay , Mindanao, Philippines, spec., 100–200 m, 1 dry spec R =4.6 r=0.6. 6-armed: CASIZ 229110 Balut Island , Philippines, 150–250 m, 1 dry spec ., R =4.1 r=0.6, taken from longest arm, 6 arms, uneven lengths). Mah PH06, Balut Island, Philippines, 200 m, PH06, 1 dry spec ., R =5.3 r=0.8 (one arm bifurcated).

Figures

FIGURE 9. Hyalinothrix vitrispinus n. sp. Holotype, NSMT-E6916. A. Abactinal surface. Scale bar=1.0 cm. B. Close-up of abactinal paxillae. Scale bar=1.0 mm. C. Oral surface. Scale bar=1.0 cm. D. Close-up of actinal surface, adambulacral plates and accessories. Scale bar=0.5 cm.