Tamaria tenella ( Fisher, 1906 )

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 : 17-19

Tamaria tenella ( Fisher, 1906)

[Japanese name: Birodo-hime-hokiboshi]

( Figs 2E , 7 )

Ophidiaster tenellus Fisher, 1906: 1082 .

Ophidiaster sp.: McKnight 1975: 56–57.

Tamaria tenellus: McKnight 1993: 172–173 .

Tamaria tenella: H. L. Clark 1921: 88 , 91; A. M. Clark 1993: 354; McKnight 2001: 176–177; Arai et al. 2018: 198–199.

Material examined. NSMT E-8285, 1 individual, coll. by Dr. Minoru Imajima in 1969, labeled as “Hyotan-jima, Ogasawara Islands , intertidal” but probably a mislabeled specimen collected by a coral fisherman Akio Kihara around Ani-jima , Chichi-jima , Haha-jima or Yome-jima Island in depth ranging from 150 to 160 m (see Imajima 1970: 190) . NSMT E-9277, 1 individual, SY-09-21, West of Ototojima Island , 159– 161 m .

Description. R=30.0 mm, r= 6.2 mm, R/r=4.8, width of arm is 7.3 mm at base, 4.6 mm at half of R, and 3.0 mm at 1/10 R from the tip in NSMT E-8285. R=26.0 mm, r= 5.4 mm, R/r=4.8, width of arm is 6.7 mm at base, 3.6 mm at half of R, and 2.1 mm at 1/10 R from the tip in NSMT E-9277. Body is arched on the abactinal side and flat on the actinal side. Arms are five and tapering toward the tip evenly from the base ( Fig. 7A ).

Abactinal plates are four-lobed and arranged in three regular longitudinal rows which reach the tip of arms. The rows are partly disrupted at base of an arm of NSMT E-8285, and the shortest arm of NSMT E-9277. Five to six carinal plates in the middle of arms and a few distal actinolateral plates are devoid of skin and granules in an elevated circular area at the center ( Fig. 7F ). Madreporite is circular, not elevated from the abactinal surface of disc; gyri radiate from the center in a complex pattern. Tubefeet are biserial with a terminal disc. Terminal plates are spherical, devoid of granules, and bearing about ten tubercles at the apex in NSMT E-9277 ( Fig. 7F ). In NSMT E-8285, the tubercles are very low and faint, and the number is about three.

Superomarginal and inferomarginal plates are similar in shape and size to abactinal plates, and arranged in two regular longitudinal series. Distal superomarginal plates (twelve to thirteen plates from the arm tip in NSMT E-9277 and seven to nine in NSMT E-8285) are devoid of a skin and granules like some of the abactinal plates ( Fig. 7F ). More distal plates have a larger, more swollen and more elliptical naked area. In NSMT E-8285, three to four distalmost inferomarginal plates are denuded and swollen like distalmost superomarginal plates.

Actinal plates are rectangular and arranged in three longitudinal series at the base of arms: the innermost series reach about 3/4R, the outer 1/2R, and the outermost 1/6R in NSMT E-8285 (in NSMT E-9277, there are two series reaching 2/3R and 1/4R respectively, and a few interradial plates).

Each adambulacral plate bears two furrow spines and a subambulacral spine ( Fig. 7D ). Furrow spines are truncated, flattened, and polygonal but rounded at corners and slightly concave at the furrow surface. Each plate carries a pair of subequal spines. Subambulacral spines are obovate but more circular in the distal part of arms. Between two furrow spines and a subambulacral spine, there are granules one of which is occasionally larger than the surroundings to appear like a tubercle.

Oral plates are covered with granules like actinal plates. A plate bears five to six oral spines and a suboral spine ( Fig. 7B ). They are identical in shape to furrow spines and subambulacral spines respectively.

The entire body is overlaid with a skin except some abactinal plates and distal superomarginal plates as mentioned above. The skin is covered with fine granules homogenous in size ( Fig. 7B, C ). The number of granules per square millimeter is 379 on proximal carinal plates and 167 on proximal actinal plates in NSMT E-9277; 281 and 295 respectively in NSMT E-8285.

A papular area bears one to three pores on the disc and one to five on the arms. The areas occur between carinal, abactinolateral, superomarginal and inferomarginal plates but never below the inferomarginal plates. They are arranged in six longitudinal series although the numbers of pores change irregularly.

Pedicellariae presents on superomarginal plates (from the base to the middle of arms), abactinal interradial plates, and exceptionally on an abactinolateral plate in NSMT E-9277, on actinolateral, superomarginal, and inferomarginal plates in NSMT E-8285. Each pedicellaria with two valves, which fit in an entrenched piece of ossicle with an alveolus at the center ( Fig. 7E ). The ossicle is merged with the subjacent plate. The valve is gradually broadening from the base to form a smooth, unserrated, and slightly curved contour.

Color in life is unknown. The ex-ethanol specimens show brown transverse bands on arms with darker papular areas and transverse lines between plates on the abactinal surface.

DNA sequence. A partial sequence of COI (655 bp) was sequenced from NSMT E-9277 and deposited in DDBJ (Acc. No. LC427076 ).

Remarks. Fisher (1906) described two closely similar species, Ophidiaster sclerodermus Fisher, 1906 and O. tenellus , distinguishing them by the length of arms, granulation, thickness of skin, number of papular pores in each area, and number of pedicellariae. Both species were subsequently transferred to the genus Tamaria by H. L. Clark (1921). The present Ogasawara specimens resemble these two species, but show discordance in some characters from each species. Tamaria scleroderma has a larger number of papular pores (9–14) and shorter arms (R/r=4.8) than Tamaria tenella . The Ogasawara specimens are consistent with T. tenella in the number of papular pores (1–3) while it has longer arms (R/r=6.9). The New Zealand specimens of T. tenella described by McKnight (1975, 2001) differ from the Ogasawara specimens in the proportion of arms, number of papulae, distribution of pedicellariae, and spines on actinal plates. The rays are longer in proportion to the disc: R/r=5.5 at R= 22 mm and 7.5 at R= 48 mm. All the papulae are isolated, and the pedicellariae occur on actinal plates. In the larger specimen with R= 48 mm, spines similar to the subambulacral ones occur on some actinal plates. In addition to these differences, the Ogasawara specimens also have a central naked area on the distal carinal and superomarginal plates which is not present in the Hawaiian or New Zealand specimens. The present specimens are temporarily considered to be T. tenella , based on the small number of papular pores per area. However, we believe that these species require a detailed revision in regard to morphological variation with a greater number of specimens.

Distribution. Hawaii Islands, 238–276 m ( Fisher 1906). Three Kings Rise and Norfolk Ridge, New Zealand, 403– 503 m ( McKnight 1993, 2001). Ogasawara Islands , Japan, 159–161 m ( Arai et al. 2018; this study).

Japanese name. Birodo means velvet, referring to the smooth skin with minute granules. Hime-hokiboshi means a small comet.

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. 7. Tamaria tenella, NSMT E-9277. A, actinal side; B, actinal surface around mouth; C, proximal portion of ray; D, proximal adambulacral plates. Right to arm tip; E, pedicellaria on the abactinal interradial plate; F, distal portion of the arm, oblique lateral view. Arrow indicates bare area on superomarginal plate. Scale bars: 10mm (A), 1mm (B, C), 500µm (D, E), 5mm (F).