Ophiozonella cavernalis, Okanishi & Fujita, 2018

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), Zootaxa 4377 (1), pp. 1-20 : 11-18

publication ID	https://doi.org/ 10.11646/zootaxa.4377.1.1
publication LSID	lsid:zoobank.org:pub:FE92756E-2212-4ADE-9FE0-31C30511583E
DOI	https://doi.org/10.5281/zenodo.3509141
persistent identifier	https://treatment.plazi.org/id/0393AD4F-FFC9-3413-FF1A-FC3FFDC9FD7B
treatment provided by	Plazi
scientific name	Ophiozonella cavernalis
status	sp. nov.

Treatment

Ophiozonella cavernalis n. sp.

[Japanese Name: Dohkutsu-mozaiku-kumohitode] ( Figs 7–11 View FIGURE7 View FIGURE 8 View FIGURE 9 View FIGURE 10 View FIGURE 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 View FIGURE 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 View FIGURE7 ; 8A). Aboral surface with imbricating polygonal and flat scales, approximately 200–400 µm in length at periphery ( Fig. 8B View FIGURE 8 ) and approximately 300–500 µm in length at center ( Fig. 8C View FIGURE 8 ). Radial shields broadly triangular, approximately 800 µm in width and 500 µm in length, separated by 2 or 3 scales ( Fig. 8B View FIGURE 8 ). 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 View FIGURE 8 ). Oral plates small, obscured by thin skin ( Fig. 8E View FIGURE 8 ). 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 View FIGURE 8 ). All oral shields similar in size and shape, and oral shield serving as madreporite unrecognizable in external view ( Fig. 8E–F View FIGURE 8 ). Interradial oral disc also covered by polygonal and imbricating scales, approximately 200–350 µm in length, approximately 30 in number ( Fig. 8F View FIGURE 8 ). A scale on midline of lateral edge larger, approximately 600 µm in length ( Fig. 8F View FIGURE 8 ). Genital slits long, narrow, almost extending to the disc edge, approximately 0.1 mm wide ( Fig. 8F View FIGURE 8 ). Four oral papillae at edge of each oral plate, 3 triangular proximal papillae, distal most wider and oblong ( Fig. 8E View FIGURE 8 ). Teeth triangular, pointed, forming vertical row on dental plate. Second tentacle pore completely inside mouth slit ( Fig. 8E View FIGURE 8 ).

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 View FIGURE 9 ).

Each arm segment externally composed of a dorsal arm plate, 2 lateral arm plates and a ventral arm plate ( Fig. 9A, D, G View FIGURE 9 ). Dorsal arm plate fan-shaped on proximal portion of arm, rounded on distal edge ( Fig. 9A View FIGURE 9 ), sharply triangular on middle portion of arm, slightly separated by lateral arm plates ( Fig. 9B View FIGURE 9 ), decreasing in size toward the arm tip and finally disappearing ( Fig. 9C View FIGURE 9 ). 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 View FIGURE 9 ). Ventral arm plate square with rounded distal edge, contiguous, almost as long as wide on proximal portion of arm ( Fig. 9D View FIGURE 9 ), triangular, rounded on distal edge, longer than wide ( Fig. 9E View FIGURE 9 ), decreasing in size toward the arm tip and finally disappearing ( Fig. 9F View FIGURE 9 ). Tentacle pores along entire arm ( Fig. 9D–F View FIGURE 9 ). Two oval, flat tentacle scales at each tentacle pore, almost the same size on proximal portion of the arms ( Fig. 9D View FIGURE 9 ). On middle portion of arm, tentacle scales oval and flat decreasing in number to 1 scale at each tentacle pore ( Fig. 9E View FIGURE 9 ). Tentacle scales decreasing in size toward the arm tip and finally disappearing ( Fig. 9F View FIGURE 9 ). Three conical arm spines, almost the same length as the corresponding arm segments on proximal portions of arms ( Fig. 9G View FIGURE 9 ). 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 View FIGURE 9 ). On distal portion of arm, arm spines become ovoid, pointed, decreasing in number to 1 on distal arm tip ( Fig. 9F View FIGURE 9 ).

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 View FIGURE7 ) and approximately 200–450 µm in length at center ( Fig. 7D View FIGURE7 ). Radial shields broadly triangular, approximately 500 µm in width and 700 µm in length, separated by 2 or 3 scales ( Fig. 7D View FIGURE7 )

Description of ossicle morphology (A paratype, RUMF-ZE-02009). Dorsal arm plates triangular, nearly as long as wide throughout arm ( Fig. 10A, C View FIGURE 10 ). A small knob present on proximal tip of dorsal arm plate at proximal portion of arm ( Fig. 10A View FIGURE 10 ). 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 View FIGURE 10 ); distal portion of arm, plates approximately 4 times longer than high, oral and aboral edges both straight ( Fig. 10H–I View FIGURE 10 ). 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 View FIGURE 10 ). External oral spur slightly larger than aboral spur. Such spurs disappear on distal portion of arm ( Fig. 10H–I View FIGURE 10 ). Bands of conspicuous, fine, horizontal striation on proximal edge ( Fig. 10D View FIGURE 10 ), such bands disappearing on distal portion of arm ( Fig. 10H View FIGURE 10 ). Three equal-sized spine articulations on distal edge ( Fig. 10D, F, H, J View FIGURE 10 ), composed of parallel, horizontal dorsal and ventral lobes ( Fig. 10G View FIGURE 10 ). Both lobes almost the same length on proximal portion of arm ( Fig. 10G View FIGURE 10 ) and ventral lobes slightly larger than dorsal lobes on distal portion of arm ( Fig. 10K View FIGURE 10 ).

On inner side, 2 large, well defined, horizontally elongated elevated structures on proximal edges ( Fig. 10E, I View FIGURE 10 ). Elevated structure almost the same width throughout arm ( Fig. 10E, I View FIGURE 10 ). Distal edge concave, with 2 well defined, oval, horizontally elongate spurs ( Fig. 10E View FIGURE 10 ). Oral spur slightly wider than aboral one, on proximal portion of arm ( Fig. 10E View FIGURE 10 ). Spurs absent on distal portion of arm ( Fig. 10I View FIGURE 10 ). 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 View FIGURE 10 ). On proximal portion of arm, a single perforation ( Fig. 10E View FIGURE 10 ) absent on distal portion of arm ( Fig. 10H View FIGURE 10 ). Ventral arm plates longer than wide, sharply triangular, notched laterally ( Fig. 10L. M View FIGURE 10 ), notches deeper on proximal portion of arm.

Vertebrae with zygospondylous articulation, elongate, large wing-like muscle flanges distally and proximally ( Fig. 11A–B View FIGURE 11 ). Muscle flanges of distal portion of arm narrower and longer than those of proximal portion of arm ( Fig. 11A–D View FIGURE 11 ). Longitudinal straight groove on both aboral and oral side ( Fig. 11C–D View FIGURE 11 ). A longitudinal large hole opening on median line on distal portion of the arm ( Fig. 11H View FIGURE 11 ). No distinct radial water/nerve canals observed from oral view ( Fig. 11D, H View FIGURE 11 ). Depression for tentacles on lateral distal side of vertebra ( Fig. 11D, H View FIGURE 11 ). On proximal portion of the arm, thin flange covering aboral side of depression partly perforated ( Fig. 11E View FIGURE 11 ).

Arm spines cylindrical, with blunt tip on proximal portion of arm ( Fig. 11I View FIGURE 11 ), narrow, with slightly thorny tip on middle portion of arm ( Fig. 11J View FIGURE 11 ), hook-shaped, with several, 3 or 4, secondary teeth on inner side on distal portion of arm ( Fig. 11K View FIGURE 11 ). Spines with simple and fine stereom without minute thorns ( Fig. 11I –K View FIGURE 11 ).

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 View FIGURE7 ).

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 View FIGURE7 ).

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 View FIGURE 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 View FIGURE7 ). 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 View FIGURE 8 , 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.