Asteroporpa (Asteromoana) koyoae, Okanishi, Masanori & Fujita, Toshihiko, 2011

Okanishi, Masanori & Fujita, Toshihiko, 2011, Two new species of the subgenus Asteroporpa (Asteromoana) (Ophiuroidea: Euryalida: Gorgonocephalidae) from Japan, Zootaxa 2751, pp. 25-39 : 33-34

Asteroporpa (Asteromoana) koyoae sp. nov.

[New Japanese name: Koyo-moana-moduru] ( Figs 6–9 )

Type materials. NSMT E- 6341-A, holotype and NSMT E- 6341-B, one paratype, collected by the R/V Koyo, south of Chichi-jima Island, Ogasawara Islands, southern Japan, 26˚53.690’N, 142˚14.321’E, 743.1 m deep, 24 July 2008 ( Fig. 1 ).

Diagnosis. Dermal ossicles are plate-shaped and cone-shaped on radial shields; cone-shaped with one or two terminal projections, on the oral plate; cone-shaped with one or two relatively long terminal projections, on the lateral interradial disc.

Description of holotype. Size is 9.4 mm in disc diameter, 44 mm in arm length ( Fig. 6 A–B).

Disc. Disc is five-lobed in shape with strongly notched interradial edges ( Fig. 6 A–B). On the aboral side, radial shields and their surrounds are conspicuously tumid ( Fig. 6 A, C). There are no conspicuous ridges of rows of raised hooklet-bearing plates, instead two or three hooklet-bearing plates are scattered on periphery of each radial shield. Each hooklet-bearing plate possesses seven or eight tubercle-shaped articulations for hooklets. Each hooklet has two or three inner teeth. Except for hooklet-bearing plates, the aboral periphery of the disc is covered both by flat, round plate-shaped dermal ossicles and by cone-shaped dermal ossicles ( Fig. 6 C–D). The flat and round plateshaped dermal ossicles, of approximately 180–280 µm in length and 140µm in height, are present only on the peripheral part of radial shields ( Fig. 6 D). The cone-shaped dermal ossicles have two to five terminal projections which in length are approximately half length of the height of the cone-shaped dermal ossicles. The cone-shaped dermal ossicles are approximately 150–220 µm in length and 220 µm in height around the periphery of the disc ( Fig. 6 C), and approximately 190–220 µm in length and 260 µm in height in the center of the disc ( Fig. 6 E). Radial shields, completely concealed by dermal ossicles, are oval in shape, approximately 5 mm in length and 1.9 mm in width, and do not reach the disc center ( Fig. 6 A).

The oral surface of the disc is covered both by flat, polygonal plate-shaped dermal ossicles and by cone-shaped dermal ossicles with one to three terminal projections, similar to those on the aboral periphery of the disc ( Fig. 6 F– G). The cone-shaped dermal ossicles are scattered on the periphery of the disc and on oral plates ( Fig. 6 F–G). The plate-shaped dermal ossicles are approximately 190–260 µm and 120µm in height ( Fig. 6 G). The cone-shaped dermal ossicles are approximately 190–260 µm in length and 140 µm in height on the oral periphery of the disc and approximately 80–120 µm in length and 100 µm in height on the oral plates ( Fig. 6 G). Oral shields, adoral shields, oral plates and ventral arm plates are concealed by dermal ossicles ( Fig. 6 F). Uniformly acute spiniform teeth and spine-formed teeth are situated on the jaws. The length of the teeth are different depending on their location on the jaw. At the top of the jaws, they are approximately 300 µm in length, and toward the base, the teeth gradually decrease in length to approximately 200 µm ( Fig. 6 H).

The lateral interradial surface of the disc is slightly inclined to the oral side and covered both by slightly-round plate-shaped dermal ossicles and by cone-shaped dermal ossicles with two to three terminal projections similar to those on oral surface of the disc ( Fig. 7 A). The plate-shaped dermal ossicles are approximately 100–150 µm in length and 100 µm in height. The cone-shaped dermal ossicles are approximately 190–210 µm in length and 360 µm in height. The terminal projections of the cone-shaped dermal ossicles are approximately 1.5 times as long as the height of the ossicles ( Fig. 7 A). Two genital slits (0.33 mm long and 0.19 mm wide) are present in each interradius. One hemispherical madreporite is situated on oral interradius, approximately 420 µm in diameter ( Fig. 7 B).

Arms. Arms are simple, five in number, have no abrupt gap in thickness ( Fig. 6 A–B). The basal portion of the arm is 2.2 mm wide and 2.1 mm high, with an arched aboral surface and flattened oral surface. Arms tapers gradually toward the arm tip ( Fig. 7 C–H).

On the aboral and lateral surface, each arm segment is surrounded by single annulated transverse rows of hooklet-bearing plates ( Fig. 7 C, E, G–H). Those hooklet-bearing plates are completely contact with each other throughout the arms. Each hooklets on the basal one fourth of the arm bear two or three inner teeth. Toward the distal portion of the arm, the number of inner teeth decreases to two. The aboral and lateral surfaces of the basal arm, except for hooklet-bearing plates, are completely covered by polygonal to diamond-shaped dermal ossicles of approximately 130–230 µm in length and 200 µm in height ( Fig. 7 C). The oral surface is covered by plate-shaped dermal ossicles similar to those on oral surface of the disc, approximately 130–240 µm in length and 120 µm in height. In the middle portion of the arm, the aboral and lateral surfaces are covered by slightly domed and round plate-shaped dermal ossicles of approximately 100–150 µm in length and 130 µm in height. The oral surface is covered by flat and polygonal plate-shaped dermal ossicles of approximately 90–120 µm in length and 120 µm in height ( Fig. 7 F–G). On the distal portion of the arm, the aboral and lateral surfaces are covered by slightly domed and round plate-shaped dermal ossicles of approximately 80–120 µm in length and 90 µm in height ( Fig. 7 H). The oral surface is covered by flat and slightly round plate-shaped dermal ossicles of approximately 60–100 µm in length and 30 µm in height. Throughout the arm, lateral arm plates and ventral arm plates are completely concealed by dermal ossicles ( Fig. 7 D, F).

The first tentacle pores have no arm spine; pores have five or six arm spines from the second to 14th or 15th. The number of the arm spines decreases gradually on subsequent segments to one toward the arm tip. Throughout the arm, all arm spines are approximately half length of the corresponding arm segment, and are covered by thin integument ( Fig. 7 D, F–H). Arm spines in the basal one-fourth of the arm are ovoid, carrying two to six terminal projections. Inner most spines have four or five terminal projections, the outer ones have two or three. In the middle one-quarter to three-quaters of the arm, arm spines are transformed into hooks; the inner most spines possess three inner teeth and the outer ones have two. On the distal quarter of the arms, the arm spines are hook-shaped and have two or three inner teeth. The hook-shaped arm spines can be distinguished from hooklets on aboral and lateral surface by having reticular structure on their basal portion.

Color. Body color is uniformly creamy white.

Ossicle morphology of one paratype. E-6341-B: Size is 8.3 mm in disc diameter, 39 mm in arm length.

Hooklet-bearing plates on the radial shield possess seven or eight tubercle-shaped articulations for hooklets ( Fig. 8 A). The tubercle-shaped articulations form two parallel rows ( Fig. 8 A). The hooklets bear two or three inner teeth ( Fig. 8 B). The hooklets on the basal portion of the arm also bear two or three inner teeth ( Fig. 8 G).

Dermal ossicles on the periphery of one radial shield are plate-shaped, approximately 180 µm in length and 200 µm in height ( Fig. 8 C–D) and are cone-shaped, approximately 180 µm in length and 200 µm in height with two to five terminal projections ( Fig. 8 E–F). The length of the terminal projections are approximately half the height of the cone-shaped dermal ossicles ( Fig. 8 E–F). Dermal ossicles on aboral basal portion of the arm are polygonal and diamond-shaped, approximately 220 µm in length and 200 µm in height ( Fig. 8 H–I).

Arm spines on the basal quarter of the arm are cylindrical, the inner ones carrying four to five terminal projections and the outer ones have two or three ( Fig. 9 A–B). Inner most arm spines on the middle to distal portion of the arms are hook-shaped, with two inner teeth along inner edge and reticular structure on basal portion ( Fig. 9 C–D).

Distribution. JAPAN: off Chichi-jima Island, the Ogasawara Islands, 743.1 m (present study), southern Japan ( Fig. 1 ).

Etymology. The specific name is named for R/V Koyo of the Ogasawara Fisheries Research Center, Japan.

Figures

FIGURE 1. Distribution of Asteroporpa (Asteromoana) muricatopatella sp. nov. and A. (Asterom.) koyoae sp. nov.

FIGURE 6. Asteroporpa (Asteromoana) koyoae sp. nov., holotype (NSMT E- 6341 - A). A, aboral disc and basal portion of the arm; B, oral disc and basal portion of the arm; C, aboral periphery of the disc; D, plate-shaped dermal ossicles at the periphery of the radial shield; E, aboral central part of the disc; F, oral disc; G, periphery of the oral disc, a cone-shaped dermal ossicle is indicated by an arrow; H, a jaw.

FIGURE 7. Asteroporpa (Asteromoana) koyoae sp. nov., holotype (NSMT E- 6341 - A). A, lateral interradius of the disc; B, a madreporite; C, aboral view of basal portion of the arm; D, oral view of basal portion of the arm; E – G, middle portion of the arm, aboral view (E), oral view (F) and lateral view (G); H, lateral view of distal portion of the arm. Abbreviations: AS, arm spine; GS, genital slit; M, madreporite. Arrows indicate transverse rows of hooklet-bearing plates (C, E, G – H).

FIGURE 8. Asteroporpa (Asteromoana) koyoae sp. nov., one paratype (NSMT E- 6341 - B). SEM photographs of internal ossicles. A – B, a hooklet-bearing plate (A) and a hooklet (B) at the aboral periphery of the disc; C – D, plate-shaped dermal ossicles at the periphery of the radial shields, external (C) and lateral (D) views; E – F, cone-shaped dermal ossicles at the aboral periphery of the disc, external (E) and lateral (F) views; G, a hooklet at the basal portion of the arm; H – I, diamond-shaped dermal ossicles at the aboral basal portion of the arm, external (H) and lateral (I) views. Arrows indicate the orientation (D, F, I): ext, external side; int, internal side.

FIGURE 9. Asteroporpa (Asteromoana) koyoae sp. nov., one paratype (NSMT E- 6341 - B). SEM photographs of arm spines. A – B, arm spines from one tentacle pore at the basal portion of the arm, inner most (A) and outer most (B); C, outer most arm spine at the middle portion of the arm; D, an arm spine at the distal portion of the arm with an arc indicating reticular structure.