Fromia labeosa, Arai & Fujita, 2021

Arai, Mikihito & Fujita, Toshihiko, 2021, Sea Stars of Families Ophidiasteridae and Goniasteridae (Echinodermata: Asteroidea) from the Mesophotic Zone of the Ogasawara Islands, Including Two New Species, Species Diversity 26 (1), pp. 7-21 : 13-15

Fromia labeosa sp. nov.

[New Japanese name: Ogasawara-juzuberi-hitode]

( Figs 2C , 5 )

Fromia sp.: Arai et al. 2018: 194, 196.

Material examined. Holotype: NSMT E-9297, KY-16-14, East of Ototo-jima Island , 56.6–62.9 m . Paratypes: NSMT E-9293, KY-08-25, West of Nishi-jima Island, 127–129 m; NSMT E-9294 and E-9295, KY-16-06, Northwest of Ototojima Island, 135–137 m; NSMT E-9296, KY-16-09, East of Chichi-jima Island, 90.5–94.6 m; 1 individual each.

Diagnosis. A species of the genus Fromia with a small disc and slender, slightly arched arms. At R= 31.3 mm, abactinal plates arranged in five longitudinal rows at base of arms. Superomarginal plates only slightly convex, not alternating but regularly decreasing in size toward the tip of arms. Coarse granules enlarged at center of plates. Papulae single and confined on the abactinal surface. Adambulacral plates bear three (rarely two or four) furrow spines and five to nine thicker subambulacral granules graduating in size toward those on neighboring actinal/marginal plates. Oral plates bear five oral spines on the margin and four to six suboral spines on the rest of the plate. Large, elliptical pedicellariae on many actinal plates with their major axis oblique to the ambulacra.

Description of holotype. R= 31.3 mm, r= 8.6 mm, R/r= 3.6, width of arm is 9.0 mm at base, 5.4 mm at half of R, and 2.9 mm at 1/10 R from the tip. Body is slightly arched at both sides, and the abactinal interradial areas are sunken. Arms taper to blunt tips.

Abactinal plates are polygonal, weakly lobate, arranged in staggered longitudinal series where there are five rows at the base of arms ( Fig. 5C ). Hemispherical glassy bosses (crystal bodies) occur on the abactinal plates. Madreporite is single, circular, and about 0.9 mm in diameter, located at about one half r from the anal aperture. Gyri do not regularly radiate from the center of the madreporite. The anal aperture is single and surrounded by six slightly larger ossicles. Terminal plates are conical, truncated at the tip. Several tubercles encircle the top of terminal plates.

Superomarginal and inferomarginal plates are block-like, rectangular, only slightly convex and not alternating but regularly decreasing in size toward the tip of arms. There are sixteen superomarginal and seventeen inferomarginal plates on one side of the ray when skin and granules are removed. The second to fourth superomarginal plates average 1.7 mm in length.

Actinal plates are polygonal, without lobes, and leave no space in between. No glassy bosses occur on actinal plates. These are arranged in three longitudinal series at the base of a denuded arm with a few odd plates on the interradial area.

Adambulacral plates bear three (exceptionally two or four), slender, flattened, cylindrical and bluntly pointed furrow spines and five to nine thicker, more sharply pointed subambulacral granules ( Fig. 5F ). The latter are not in regular rows parallel to the ambulacrum, and are grading in size to the granules on neighboring actinal or marginal plates. Tubefeet are biserial with a stout terminal disc.

Each oral plate bears five oral spines on the adoral margin and four to six suboral spines on the rest of the plate. Oral spines are conical or pyramidal, larger than furrow spines. Suboral spines are similar to oral spines in the adradial portion but abradially grading into actinal granules.

The abactinal, marginal, and actinal plates are concealed with a skin which is covered coarsely with granules ( Fig. 5B ). These granules are domed at the top, polygonal in shape, and slightly enlarged at the center of plates, but never spinous. The diameter is ca. 260–340µm at center and ca. 140–200µm on periphery. There are 20 granules per square millimeter on abactinal plates at the base of arms and actinal interradial plates. The papular pores are isolated and confined around abactinal plates except on the interradial areas and tips of arms, where the pores are absent.

Many actinal plates possess a large elliptical pedicellaria ( Fig. 5D ). It is typically 1 mm in length and 400 µm in width. The pedicellariae are loosely arranged in a parallel series to an ambulacrum on arms, and their major axis is often oblique to the ambulacrum ( Fig. 5A, E ).

Color in life is vermilion with white granules and terminal plates ( Fig. 2C ).

Notes on paratypes. The difference in the numeric characters among type specimens is shown in Table 2. R /r generally increases and the number of granules per square millimeter decreases as R increases. Other characters in the paratypes are consistent with the description of holotype.

DNA sequence. A partial sequence of COI (655 bp) was obtained from NSMT E-9295 and deposited in DDBJ (Acc. No. LC427074 ).

Remarks. The present species is distinguished from its congeners by the following characters: superomarginal plates regularly decreasing in size toward the arm tip in F. labeosa sp. nov. while they are alternating large and small, or small superomarginal plates are occasionally intercalated between larger ones, in F. pacifica H. L. Clark, 1921 , F. heffernani (Livingstone, 1931) , F. monilis (Perrier, 1869) , and F. nodosa A. M. Clark, 1967 ; there are five abactinal plates between first superomarginal plates on each side of arms in F. labeosa while there are more than seven such plates in F. hemiopla Fisher, 1913 , F. milleporella (Lamarck, 1816) , F. polypora H. L. Clark, 1916 , and F. schultzei (Döderlein, 1910) ; abactinal plates are uniform in size in F. labeosa while several elliptical plates are larger than others in F. elegans H. L. Clark, 1921 and F. indica (Perrier, 1869) ; abactinal granules are granular in F. labeosa while they are spinuous in F. armata Koehler, 1910 ; they are also coarse (20/mm 2) in F. labeosa while they are fine (80–90/mm 2) in F. hadracantha H. L. Clark, 1921 ; papulae are lacking on the actinal surface in F. labeosa while there are two rows of actinal papulae in F. balansae Perrier, 1875 and F. ghardaqana Mortensen, 1938 . Five to nine subambulacral tubercles continuous in size and not arranged in definite rows in F. labeosa while subambulacral spines are conspicuously larger than outer granules on the adambulacral plate, and arranged in a straight row in F. eusticha . In addition to these differences, large elliptical pedicellariae on actinal plates are specific to F. labeosa .

Distribution. Ogasawara Islands , 56.6–137 m (this study).

Etymology. The species epithet, labeosa , is a Latin feminine adjective meaning having large lips and referring to the large pedicellariae on the actinal surface.

Japanese name. Ogasawara is taken from the type locality and juzuberi-hitode is a Japanese name for the genus Fromia .

Figures

Fig. 2. Abactinal view of the live specimens (A–D) and ethanol-preserved specimen (E). A, Bathyferdina caelator sp. nov., NSMT E-8265, holotype; B, Fromia eusticha, NSMT E-10595; C, Fromia labeosa sp. nov., NSMT E-9297, holotype; D, Ogmaster capella, NSMT E-9312; E, Tamaria tenella, NSMT E-9277. Scale bars: 10mm.

Fig. 5. Fromia labeosa sp. nov., NSMT E-9297, holotype. A, actinal surface of the disc; B, abactinal surface of interradial area showing a madreporite (arrow); C, abactinal surface of a denuded arm; D, pedicellaria on the actinal plate; E, proximal portion of a partly denuded arm, actinal side. Arrows indicate pedicellariae; F, adambulacral armature on proximal adambulacral plates. Scale bars: 5mm (A, C), 1mm (B, E), 500µm (D, F). Abbreviations: fs, furrow spines; ss, subambulacral spines.