Hyalinothrix diversus, 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 : 84-86

Hyalinothrix diversus n. sp.

Figure 5 A–F

Etymology: The species epithet is derived from the Latin diversus for different or separate alluding to the many differently shaped abactinal paxillae present on the disk.

Diagnosis. A stellate species (R/r=5.4 to 6.5) with tapering arms, thick disk and flat oral surface. Variably shaped abactinal paxillae, especially on the disk, with 10–60, mostly 20–40 glassine spinelets abactinal spinelets, each with multispinous glassine tips. Marginal plates similar to abactinal plates, each bearing 40–60 densely packed spinelets. Actinal plates each with 8–15 short, papillate spinelets. Furrow spines 4 to 6 in palmate arrangement. Subambulacrals, 5 to 9, blunt, elongate in a single transverse series, set off from furrow spines by discrete space.

Second subambulacral spine cluster with 10-15 blunt spines.

Comments. Although this species displays paxillae, its thick disk and arms and relatively flattened actinal surface suggest a comparison with the asterinid Nepanthia . This species is similar to Hyalinothrix grangei nov. comb., in that several of its characters suggest intermediate morphology between Hyalinotrix and Nepanthia . Structures, such as the “paxillae” in Hyalinothrix and the “subpaxillar” plates in asterinids such as Paranepanthia grandis (see O’Loughlin & Waters 2004: fig. 5c) show distinction mainly based on elongation of the plate above the base.

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

Description. Body strongly stellate (R/r=5.4 to 6.5), arms tapering, forming isosceles trapezoid in cross-section, oral surface flat, disk thick ( Fig. 5A ).

Abactinal plate arrangement forming distinct round papular pores between paxillar plates. Individual plates ovate to quadrilobate, imbricate distally forming more fenestrate skeleton proximally ( Fig. 5B ). Well developed fasciolar grooves present. Plates with paxillar spines and raised ridges, both forming fasciolar grooves between them, but individual plates highly varied in shape. Disk plates vary in outline from round, trigonal, quadrate to polygonal. Plates on arm primarily oval to round to quadrate or polygonal in shape becoming more homogeneous distally. Short, glassine spinelets, 10–60, mostly 20–40, equal to or shorter to the length of paxillae densely to evenly distributed, present on each disk-radial region plate ( Fig 5C ). Abactinal paxillae broadly separated into a disk and central radial region and a lateral-interradial on disk region. Disk-radial abactinal paxillae in irregular series individual paxillae are heterogeneous in shape and size, with some smaller plates 25% of the size of other larger plates. Five primary disk plates present at the apex of each interradius, each about three times the size of adjacent smaller paxillae. Lateral plate fields begin interradially from the primary plates on the disk, forming linear, transverse series extending from the contact with the radial/disk plate field to the superomarginal plate series. These lateral arm plate fields are round to polygonal in outline with rounder, smaller plates present adjacent to the superomarginal series. Lateral fields include multiple series proximally decreasing to a single series distally, running parallel to the superomarginals. Papulae irregular but present on both radial and lateral fields, more abundant proximally, becoming less so distally and finally disappearing near armtip. Madreporite, weakly convex to flat, obscured by three or four adjacent paxillae, with well-developed sulci.

Marginal plates, approximately 120–130 per interradius (60–65 per arm), plates are paxillar, identical to those on adjacent “lateral” plate field, oval to polygonal in shape topped by 40–60 sharp densely packed spinelets ( Fig. 5E ). Superomarginals show 1:1 association with inferomarginals. Well-developed fasciolar grooves present between marginal plate series.

Actinal plates in three or four series on disk, one or two series present proximally on arms, pinching out basally. Actinal plates papillate with eight to 15 blunt, short spinelets; fasciolar grooves well-developed.

Furrow spines blunt, four to six, mostly four or five (at R=3.0 to 4.0) in palmate arrangement, with proximal most spines shortest relative to the longer medial to distal furrow spines ( Fig. 5F ). Largest individual (R=7.4) with five spines on most proximal adambulacral plates, six on distalmost plates. Furrow spines are set deeply into tube foot furrow. Subambulacrals blunt, elongate, five to nine, mostly five to seven, variably in a single transverse series, or a cluster set off from furrow spines by a discrete space. A second subambulacral spine cluster, including 10–15 blunt spines is adjacent to the actinal plate contact and more closely resembles an actinal paxillar plate. Oral plate furrow spines seven (at R=~4.0), eight or nine at R=7.0, forming fully convex curve around edge of oral plate projecting into mouth. Oral plate surface with two low plates bearing three spines each on each plate totaling six per plate, 12 per interradius.

Material Examined. Holotype: NMEC 6915 , PH-05 Balut Island , 150–250 m, 1 dry spec., R =4.6 r=0.8

Paratypes: CASIZ 229107 , PH-01 Balut Island , 150–250 m, 1 dry spec ., R =6.5 r=1.4, CASIZ 229108 , PH-01 Balut Island , 150–250 m, 2 dry specs , R =3.9 r=0.6, R =3.8 r=0.7.

Figures

FIGURE 5. Hyalinothrix diversus n. sp. Holotype, NMEC 6915. Scale bar=1.0 cm except for C and F. A. Abactinal surface. B. Close-up of abactinal surface. C. Close-up showing abactinal-lateral paxillae transition. Scale bar=2.0 mm. D. Oral surface. E. Actinolateral edge. F. Furrow region showing adambulacral plates and spination. Scale bar=0.5 cm