Ophiolepis cavitata Okanishi & Fujita 2018, n. sp.
Creators: name: Okanishi, Masanori
name: Fujita, Yoshihisa
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Ophiuroidea
Ophiurida
Ophiolepididae
Ophiolepis
Ophiolepis cavitata

description: Ophiolepis cavitata n. sp.
[Japanese Name: Kunigami-kumohitode] (Figs 2–6)
Type material. Holotype: RUMF-ZE-02006, submarine cave (Hedo-Dome cave) at northern Okinawa Island, southwestern Japan (26˚52.14’N, 128˚14.53’E), c.a. 12 m depth, 23 May 2017, SCUBA diving, coll. Y. Fujita and M. Okanishi. One paratype: RUMF-ZE-02007 same locality as holotype, 21 May 2017 (Fig. 1).
Diagnosis. Round, prominent tubercle-shaped dorsal knobs on dorsal arm plates; the larger disc scales 3–8 times broader than smaller disc scales; larger disc scales concave; radial shields wider than long; a trio of elongate scales lying distal to each pair of radial shields; oral shields partly concave; supplementary plates alongside dorsal arm plate present on proximal 3 arm segments; lateral arm plates in contact after 9th arm segments; 3 arm spines on proximal segments of the arms.
Description of external morphology (holotype, RUMF-ZE-02006). Disc. Circular, 6 mm in diameter (Fig. 2), covered by imbricating scales of two sizes. On aboral surface, polygonal or circular larger scales, approximately 300–600 µm in length, surrounded by smaller polygonal scales, approximately 50–200 µm in length (Fig. 3A, C).
Center of each larger scale concave (Fig. 3C). Radial shields parallelogram, distal side narrower, slightly larger than larger disc scales, approximately 700 µm in length and 300 µm in width, separated by smaller scales (Fig. 3B). A trio of plates just distal to a pair of radial shields (Fig. 3B). On oral surface, adoral shields triangular, wider than long, approximately 500 µm in length, 150 µm in width inner side, 300 µm in width outer side, in contact with the first ventral arm plates (Fig. 3D–E). Oral plates triangular, approximately 200 µm in length, 180 µm in width inner side, 20 µm in width outer side, in contact with each other (Fig. 3E). Oral shields pentagonal, slightly rounded and convex on distal side, approximately 500 µm in length, 400–600 µm in width, and concave proximally (Fig. 3D). All oral shields similar in size and shape, oral shield serving as madreporite unrecognizable in external view (Fig. 3E). Interradial oral disc also covered by larger scales, approximately 250–450 µm in length and smaller scales, approximately 80–150 µm in length, as those on aboral disc (Fig. 3F). Genital slits long, almost extending to the disc edge and narrower, approximately 0.01 mm (Fig. 3E), approximately 10 parallel ornaments on distal side of each genital plate. Three, subequal trapezoidal oral papillae at each oral plate, and 2 polygonal oral papillae, inner one wider than outer one, at each adoral shield (Fig. 3E). Teeth triangular, pointed, forming vertical row on dental plate. Second tentacle pore completely inside the mouth slit.
Arms. Five in number, 15–17 mm in length, 1.2 mm wide and 0.6 mm high (excluding the dorsal knobs), in proximal portion, square in section. Arms tapering gradually toward the arm tip (Fig. 2).
Each arm segment carrying a dorsal arm plate, 2 lateral arm plates and a ventral arm plate (Fig. 4). On proximal portion of the arm, dorsal arm plates sharply triangular, in contact with each other (Fig. 3H). Each dorsal arm plate carrying 2 small supplementary plates which disappear after 4th arm segments (Fig. 3H). On middle portion of the arm, dorsal arm plates separated and gradually decreasing in size toward the arm tip (Fig. 4A–B). Dorsal arm plates essentially as wide as long throughout the arm (Fig. 3H). Each dorsal arm plate carrying a large tubercle-shaped dorsal knob at proximal portion of arm (Fig. 3H). Knobs abruptly decrease in height at middle portion of arm, disappearing on distal portion of arm (Figs 3H; 4A–B). Lateral arm plates thick, protruding from arm, widely separated by dorsal and ventral arm plates on proximal portion of arm (Fig. 3G, H), in contact with each other after 9th or 10th arm segments on both oral and aboral sides (Fig. 4A–D). Ventral arm plates triangular with slightly pointed proximal edge and with concave lateral edges, almost as wide as long, contiguous on proximal portion of arms and separated on subsequent segments (Figs 3G; 4C–D). Three short, appressed conical arm spines, about one-fifth length of the corresponding arm segment throughout the arms (Fig. 4E–F) (see detailed descriptions of each ossicle in next section). Two oval tentacle scales at each tentcale pore, inner scale smaller, approximately half length of outer scale (Figs 3G; 4C).
Description of ossicle morphology (a paratype, RUMF-ZE-02007). Dorsal arm plates sharply triangular, longer than wide on proximal portion of the arms, nearly as long as wide on distal portion of the arms (Fig. 5A–B). Lateral arm plates longer than high, oral edge straight and aboral-proximal edge slightly convex (Fig. 5C–D, G–H). In external view, proximal edge convex with 2 well defined, prominent and horizontally elongated spurs composed of more densely meshed stereom than remaining proximal edge (Fig. 5C, G). Oral external spur slightly larger than aboral one. Bands of conspicuous, fine horizontal striations on the proximal edge, almost the same length but several striations on aboral side slightly shorter (Fig. 5C, G). Three equal-sized spine articulations on distal edge (Fig. 5E, I), composed of parallel, horizontal dorsal and ventral lobes (Fig. 5F, J). Dorsal lobes basically larger than ventral lobes (Fig. 5F, J).
On inner side, 2 well defined large, horizontally elevated structures on proximal edges (Fig. 5D, H). Oral elevated structure wider than aboral on proximal portion of arm (Fig. 5D) but on distal portion of arm, aboral elevated structure wider than oral (Fig. 5H). Distal edge concave with 2 well defined, oval and slightly horizontally elongated spurs (Fig. 5D, H). Aboral spur slightly wider than oral on proximal portion of arm but of the same size on distal portion of arm (Fig. 5D, H). Spurs composed of more densely meshed stereom than remaining distal edge. Large tentacle notches opening on aboral side and end in center of lateral arm plates, where a single perforation is opening (Fig. 5D, H). Ventral arm plates basically sharply triangular, notched on lateral sides. Proximal surface shallow concavity is larger on proximal portion of arm (Fig. 5K) than on distal portion of arm (Fig. 5L).
Vertebrae with zygospondylous articulation, elongate, large wing-like muscle flanges on oral-distal side and aboral-proximal side (Fig. 6A–F). Muscle flanges on distal portion of arms narrower than those of proximal portion. Longitudinal groove on both aboral and oral side (Fig. 6C, F–G). A pair of radial water canals opening inside oral groove (Fig. 6F). Depression for tentacles located on lateral distal side of vertebra (Fig. 6F)
Arm spines short, pointed, thicker at proximal portion of arms than at distal portion of arm (Fig. 6H–I). Spines with simple and fine stereom bearing minute thorns (Fig. 6H–I).
Color in life. Creamy white. On aboral side, distal edges of larger disc scales, several lateral arm plates and dorsal arm plates pinkish. Pink or brown spots scattered on aboral disc and inner edge of lateral arm plates. Brown transverse bands on two arm segments every five arm segments (Fig. 2). On oral side, proximal portion of arms slightly pinkish, tentacle pore especially deep pink (Fig. 2C).
Distribution. JAPAN: a submarine cave (Hedo-Dome cave) of northern Okinawa Island (Type locality, Fig. 1), ca. 45 m distance from the entrance of the cave, hyposaline 28 ppt, ca. 12 m depth, under rocks (Fig. 2A).
Etymology. The specific name is derived from the Latin adjective, cavitata meaning “concaved”, referring to the partly concaved oral shield of this new species.
Habitat. Ophiolepis cavitata n. sp. was found in a submarine cave popularly known as “Hedo-Dome cave”, located at the north coast of Okinawa Island, Ryukyu Islands, southwestern Japan. The cave’s entrance lies at 15 m below sea level, and is 14 m wide and 3 m high. The interior of the cave is about 53 m long, and is continued by a stepwise tunnel with frontage road. Although we conducted simple quantitative surveys in the Hedo-Dome cave during 21 to 23 May 2017, this new species was only found at the “silty room”, which is approximately 45 m from the entrance of the cave, with no light and low salinity (28 ppt), suggesting its anchialine environment. Successive surveys around Okinawa Islands by scuba diving have been conducted but this species has never been discovered elsewhere (e.g. Y. Fujita et al. 2015). Therefore, this new species has so far only found in Japan in the cave system. However, only 2 specimens were found in a single cave despite extensive searching, which suggests that this occurrence may have been random.
If the single specimen collected at 73 m depth off Fraser Island, Queensland, northeastern Australia (as Ophiolepis rugosa, see also “ Remarks ” of this section and Baker 1979) was proved to be conspecific with O. cavitata, this species does not indicate a cave population.
Remarks. Of the 21 extant species in the genus Ophiolepis (Stöhr et al. 2017), Ophiolepis cavitata n. sp. is most closely related to O. rugosa Koehler, 1898 and O. nodosa Duncan, 1887, both from the Indian Ocean, in having prominent tubercle-shaped knobs on the dorsal arm plates (Duncan 1887; Koehler 1898; A. M. Clark & Rowe 1971; Baker 1979; T. Fujita 2016). The present new species can be distinguished from the two related species by shapes, sizes and arrangements of disc scales, radial shields, and oral shields, locations of supplementary small plates besides dorsal arm plates, separated lateral arm plates, and number of arm spines. These characters are compared among three related species as follows:
(1) Disc scales. On the aboral surface of the disc, the larger disc scales of O. cavitata n. sp. are 3–8 times longer than the smaller scales in diameter, whereas those of O. rugosa are 2–4 times, and those of O nodosa more than 10 times longer. Just distal to radial shields, a trio of elongated scales is present in O. cavitata n. sp., whereas five distinct scales are present in a type of O. rugosa (in the Zoological Survey of India collections in Calcatta, ZSI 287/7, pers. comm. Dr. Tim O’Hara of Museum Victoria), and numerous smaller scales present in O. nodosa. The larger disc scales of O. cavitata n. sp. and O. rugosa are somewhat concave, but those of O. nodosa are strongly convex.
(2) Radial shields. Ophiolepis cavitata n. sp. and O. rugosa share similar radial shields, 2 times wider than long, widely separated by flat disc scales. Radial shields of O. nodosa are longer than wide and separated by a convex large scale.
(3) Oral shields. Oral shields of O. cavitata n. sp. are partly concave, while those of O. rugosa and O. nodosa are not concave, having flat surfaces.
(4) Supplementary plates. Two small supplementary plates accompany each dorsal arm plate within proximal 3 arm segments in O. cavitata n. sp. whereas those of O. rugosa are present throughout the arms.
(5) Lateral arm plates. A pair of lateral arm plates are in contact after 9th arm segments on the aboral side of the arm in O. cavitata n. sp. and those of O. rugosa are separated throughout the arms. These characters of arm plates in O. nodosa are not mentioned in the original description, but an illustration shows that supplementary small plates are present for at least 5 arm segments (Duncan 1887).
(6) Arm spines. Number of arm spines on the proximal portion of the arms are 3 in O cavitata n. sp. and O. rugosa, and 4–6 in O. nodosa.
Recently, Pineda-Enríquez et al. (in press) described three species of Ophiolepis. One of them is related to O. cavitata but distinguished by having a large oval scale, which cover almost oral interradial surface, and having not concaved oral shields (Pineda-Enríquez et al. in press).
Baker (1979) referred a single specimen of Ophiolepis collected in 73 m deep of northeastern Australia (AM J10989) to Ophiolepis rugosa Koehler, 1898 which is known from southwestern Sri Lanka (Koehler 1898). Baker (1979) doubted that this specimen represented an undescribed species, even though it differed from the original description of O. rugosa in having small supplementary plates on the first three arm segments, and lateral arm plates in contact after 9th arm segments (Koehler 1898; Baker 1979). In this study, our two specimens of O. cavitata n. sp. (RUMF-ZE-02006 and RUMF-ZE-02007) possesses the same features as those of Baker (1979) and his single specimen (AM J10989) may be conspecific with O. cavitata n. sp. However, we here refrain from including this specimen to our new species concept because it is merely based on a short description and some line drawings.
description: Published as part of Okanishi, Masanori & Fujita, Yoshihisa, 2018, First finding of anchialine and submarine cave dwelling brittle stars from the Pacific Ocean, with descriptions of new species of Ophiolepis and Ophiozonella (Echinodermata: Ophiuroidea: Amphilepidida), pp. 1-20 in Zootaxa 4377 (1) on pages 3-10, DOI: 10.11646/zootaxa.4377.1.1, http://zenodo.org/record/1163170