Ophiozonella cavernalis 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
Ophiozonella
Ophiozonella cavernalis

description: Ophiozonella cavernalis n. sp.
[Japanese Name: Dohkutsu-mozaiku-kumohitode] (Figs 7–11)
Type material. Holotype: RUMF-ZE-02008, submarine cave (Hedo-Dome cave) on northern Okinawa Island, southwestern Japan (26˚51’53.74”N, 128˚14’43.93”E. Fig. 1), c.a. 10 m depth, 10 August 2016, SCUBA diving, coll. By Y. Fujita.
Paratypes (18 specimens). Okinawa Island: RUMF-ZE-02011 (1 specimen), same data as holotype; RUMF- ZE-02009 (1 specimen), RUMF-ZE-02010 (1 specimen), RUMF-ZE-02012 (1 specimen), RUMF-ZE-02013 (1 specimen), RUMF-ZE-02014 (1 specimen), same locality as holotype, 12 m depth, 21 May 2017, SCUBA diving, coll. By Y. Fujita and M. Okanishi; NSMT E-10711 (2 specimens), same locality as holotype, 12 m depth, 21 May 2017, SCUBA diving, coll. By Y. Fujita and M. Okanishi. Ie Island: RUMF-ZE-02015 (5 specimens), NSMT E- 10712 (1 specimen), submarine cave (Dai-Dohkutsu cave) at northeastern Ie Island, southwestern Japan (26˚43’27.55’N, 127˚49’53.50”E), c.a. 27 m depth, 25 June 2017. RUMF-ZE-02016 (1 specimen), unnamed submarine cave at northeastern Ie Island, southwestern Japan (26˚43’26.31’N, 127˚49’54.86”E), c.a. 20 m depth, 25 June 2017, SCUBA diving, coll. By Y. Fujita. Shimoji Island: RUMF-ZE-2017 (1 specimen), submarine cave (Akuma-no-Yakata cave) at the southern Shimoji Island, Miyako-Island Group, Ryukyu Islands, southwestern Japan (24˚49’22.51’N, 125˚08’07.84”E), c.a. 20 m depth, 4 February 2017, SCUBA diving, coll. By Y. Fujita, RUMF-ZE-02018 (1 specimen), same locality and sampling data as RUMF-ZE-02017 (1 specimen); NSMT E- 10713 (1 specimen), same locality as RUMF-ZE-2017 c.a. 8 m depth, 5 February 2017; NSMT E-10714 (1 specimen), same data as RUMF-ZE-2017.
Diagnosis. Disc scales polygonal, uniform in size; oral shields almost as long as wide, shallow concave proximal sides that end in a fairly sharp point medially; arms about 9 times longer than disc diameter; 3 cylindrical arm spines, of which the oral most one is slightly larger than the other two.
Description of external morphology (Holotype, RUMF-ZE-02008). Disc. Pentagonal, 5.3 mm in diameter (Figs 7B; 8A). Aboral surface with imbricating polygonal and flat scales, approximately 200–400 µm in length at periphery (Fig. 8B) and approximately 300–500 µm in length at center (Fig. 8C). Radial shields broadly triangular, approximately 800 µm in width and 500 µm in length, separated by 2 or 3 scales (Fig. 8B). Adoral shield triangular, wider than long, approximately 550 µm in width, 200 µm in length inner side, 300 µm in length outer side, continues around the lateral angle of the oral shield, in contact with first ventral arm plates (Fig. 8D–E). Oral plates small, obscured by thin skin (Fig. 8E). Oral shields pointed proximally with slightly concave lateral proximal edges and a strongly convex distal edge, approximately 500 µm in length, 600 µm in width (Fig. 8E). All oral shields similar in size and shape, and oral shield serving as madreporite unrecognizable in external view (Fig. 8E–F). Interradial oral disc also covered by polygonal and imbricating scales, approximately 200–350 µm in length, approximately 30 in number (Fig. 8F). A scale on midline of lateral edge larger, approximately 600 µm in length (Fig. 8F). Genital slits long, narrow, almost extending to the disc edge, approximately 0.1 mm wide (Fig. 8F). Four oral papillae at edge of each oral plate, 3 triangular proximal papillae, distal most wider and oblong (Fig. 8E). Teeth triangular, pointed, forming vertical row on dental plate. Second tentacle pore completely inside mouth slit (Fig. 8E).
Arms. Five in number, 3 with evidence of regeneration, 31–37 mm in length, and 2 entire arms 41–46 mm in length, 1.6 mm wide and 1.2 mm high, arched on dorsal side and flat on ventral side. Arms tapering gradually toward the arm tip (Fig. 9).
Each arm segment externally composed of a dorsal arm plate, 2 lateral arm plates and a ventral arm plate (Fig. 9A, D, G). Dorsal arm plate fan-shaped on proximal portion of arm, rounded on distal edge (Fig. 9A), sharply triangular on middle portion of arm, slightly separated by lateral arm plates (Fig. 9B), decreasing in size toward the arm tip and finally disappearing (Fig. 9C). Lateral arm plates oblong in external view, slightly wider than high on proximal portion of arm and twice as wide as high on distal portion of arm (Fig. 9G–H). Ventral arm plate square with rounded distal edge, contiguous, almost as long as wide on proximal portion of arm (Fig. 9D), triangular, rounded on distal edge, longer than wide (Fig. 9E), decreasing in size toward the arm tip and finally disappearing (Fig. 9F). Tentacle pores along entire arm (Fig. 9D–F). Two oval, flat tentacle scales at each tentacle pore, almost the same size on proximal portion of the arms (Fig. 9D). On middle portion of arm, tentacle scales oval and flat decreasing in number to 1 scale at each tentacle pore (Fig. 9E). Tentacle scales decreasing in size toward the arm tip and finally disappearing (Fig. 9F). Three conical arm spines, almost the same length as the corresponding arm segments on proximal portions of arms (Fig. 9G). On middle portion of arms, arm spines decreasing in length to one-fourth to one-fifth the length of corresponding arm segments, oral most spine slightly longer than other 2 spines (Fig. 9H). On distal portion of arm, arm spines become ovoid, pointed, decreasing in number to 1 on distal arm tip (Fig. 9F).
Description by SEM observation (A paratype, RUMF-ZE-02009). Aboral surface with imbricating polygonal and flat scales, approximately 250–500 µm in length at periphery (Fig. 7C) and approximately 200–450 µm in length at center (Fig. 7D). Radial shields broadly triangular, approximately 500 µm in width and 700 µm in length, separated by 2 or 3 scales (Fig. 7D)
Description of ossicle morphology (A paratype, RUMF-ZE-02009). Dorsal arm plates triangular, nearly as long as wide throughout arm (Fig. 10A, C). A small knob present on proximal tip of dorsal arm plate at proximal portion of arm (Fig. 10A). Lateral arm plates on proximal portion of arm slightly longer than high, aboral edge curved to oral-distal side and oral edge shallow convex on proximal side (Fig. 10D–E); distal portion of arm, plates approximately 4 times longer than high, oral and aboral edges both straight (Fig. 10H–I). In external view, proximal edge convex with 2 well defined, prominent, horizontally elongated spurs composed of more densely meshed stereom than remaining proximal edge (Fig. 10D). External oral spur slightly larger than aboral spur. Such spurs disappear on distal portion of arm (Fig. 10H–I). Bands of conspicuous, fine, horizontal striation on proximal edge (Fig. 10D), such bands disappearing on distal portion of arm (Fig. 10H). Three equal-sized spine articulations on distal edge (Fig. 10D, F, H, J), composed of parallel, horizontal dorsal and ventral lobes (Fig. 10G). Both lobes almost the same length on proximal portion of arm (Fig. 10G) and ventral lobes slightly larger than dorsal lobes on distal portion of arm (Fig. 10K).
On inner side, 2 large, well defined, horizontally elongated elevated structures on proximal edges (Fig. 10E, I). Elevated structure almost the same width throughout arm (Fig. 10E, I). Distal edge concave, with 2 well defined, oval, horizontally elongate spurs (Fig. 10E). Oral spur slightly wider than aboral one, on proximal portion of arm (Fig. 10E). Spurs absent on distal portion of arm (Fig. 10I). Spurs composed of more densely meshed stereom than remaining distal edge. Tentacle notches opening on oral side, ending in center of lateral arm plates (Fig. 10E, I). On proximal portion of arm, a single perforation (Fig. 10E) absent on distal portion of arm (Fig. 10H). Ventral arm plates longer than wide, sharply triangular, notched laterally (Fig. 10L. M), notches deeper on proximal portion of arm.
Vertebrae with zygospondylous articulation, elongate, large wing-like muscle flanges distally and proximally (Fig. 11A–B). Muscle flanges of distal portion of arm narrower and longer than those of proximal portion of arm (Fig. 11A–D). Longitudinal straight groove on both aboral and oral side (Fig. 11C–D). A longitudinal large hole opening on median line on distal portion of the arm (Fig. 11H). No distinct radial water/nerve canals observed from oral view (Fig. 11D, H). Depression for tentacles on lateral distal side of vertebra (Fig. 11D, H). On proximal portion of the arm, thin flange covering aboral side of depression partly perforated (Fig. 11E).
Arm spines cylindrical, with blunt tip on proximal portion of arm (Fig. 11I), narrow, with slightly thorny tip on middle portion of arm (Fig. 11J), hook-shaped, with several, 3 or 4, secondary teeth on inner side on distal portion of arm (Fig. 11K). Spines with simple and fine stereom without minute thorns (Fig. 11I –K).
Color in life. Mottled light and dark brown on aboral disc, radial shields darker, arms variegated light brown with dark bands, a darker brown band on proximal portion of each arm spine (Fig. 7).
Etymology. The specific name is derived from the Latin feminine noun, cavernalis meaning “inhabits cave”, referring to the cavernicolous habits of this new species.
Distribution. JAPAN: submarine caves on the Ryukyu Islands (Okinawa and Ie Islands, Okinawa Island Group, and Shimoji Island, Miyako Island Group), 8–27 m depth (Fig. 7A).
Habitat. In the Ryukyu Islands, this new species was found in 4 submarine caves “Hedo-Dome cave” at Okinawa Island, “Dai-Dokutsu cave” and “unnamed cave” at Ie Island and “Akuma-no-Yakata cave” at Shimoji Island (Fig. 1), and anchialine environment (low salinity and water-temperature) is confirmed in all caves. At the “Hedo-Dome cave”, this species was collected together with Ophiolepis cavitata n. sp. (Fig. 7A). At the “Dai- Dohkutsu cave”, this species is densely aggregated on the sandy-muddy bottom of the cave. This species was also found in similar environments (under rock on rubble zone or sandy-muddy bottom) in the “unnamed cave” and “Akuma-no-Yakata cave”. Compared to Ophiolepis cavitata n. sp., the number of O. cavernalis specimens is large and its presence in 4 caves suggest that it is indeed a cave endemic species with self-recruiting population.
Remarks. Among 31 species of Ophiozonella s. a., the present specimens are most closely related to O. clypeata (Lyman 1883) and partly agree with the original description in morphology (Lyman, 1883). However, O. cavernalis n. sp. can be distinguished from O. clypeata on the basis of the shape of oral shields and length of arm as follows:
(1) Oral shields. The oral shields of O. cavernalis n. sp. are as long as wide, with slightly concave proximal sides that end in a fairly sharp point medially, whereas those of O. clypeata are 1.5 times longer than wide, blunt spear-head sharp, with acute proximal point (Fig. 8E, Lyman 1883).
(2) Arms. Ratio of the longest entire arm to disc diameter is 9 times in O. cavernalis n. sp. and at most 6 in O. clypeata (H. L. Clark, 1908). For examination of other 18 paratypes, the smallest number of the ratio of the longest entire arm/disc diameter was 8 times.
In conjunction with the wide separation of their distribution (O. cavernalis n. sp. is from 8–27 m, Japan and O. clypeata is from 158–559 m, Galapagos and Caribbean Sea), these two species should be distinguished as different species (Lyman 1883; H. L. Clark 1917).
Three species of Ophiozonella s. str., O. subtilis Koehler, 1922, O. insulata (Lyman, 1878) and O. casta (Koehler, 1904) with more than 3 arm spines have been recorded from Indo-Pacific. These three species can be distinguished from Ophiozonella cavernalis n. sp. mainly by the following characters: Ophiozonella subtilis has smaller and narrower oral shields; O. insulate and O. casta have approximately 15 and 10 disc scales on interradial oral surface, respectively, which are fewer than 30–50 scales of O. cavernalis (Lyman, 1878; Koehler, 1904, 1922).
The first anchialine-endemic ophiuroid species (Amphicutis stygobita) was found in Bernier Cave, Bahamas, Atlantic Ocean (Pomory et al. 2011). This is the second discovery of an anchialine-endemic ophiuroid species and the first finding from the Pacific Ocean.
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 11-18, DOI: 10.11646/zootaxa.4377.1.1, http://zenodo.org/record/1163170