A New Record of Brittle Star Ophiopsila Cf. Polyacantha (Echinodermata: Ophiuroidea) from Southwestern Japan, with Notes on Its Bioluminescence
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Species Diversity 25: 283–294 Published online 28 October 2020 DOI: 10.12782/specdiv.25.283 A New Record of Brittle Star Ophiopsila cf. polyacantha (Echinodermata: Ophiuroidea) from Southwestern Japan, with Notes on its Bioluminescence Masanori Okanishi1,3 and Takuma Fujii2 1 Misaki Marine Biological Station, Department of Science, The University of Tokyo, 1024 Koajiro, Miura, Kanagawa 238-0225, Japan E-mail: [email protected] 2 International Center for Island Studies, Kagoshima University, 15-1-6F Naze-Minatomachi, Amami, Kagoshima 894-0026, Japan 3 Corresponding author (Received 26 May 2020; Accepted 23 July 2020) Two specimens of Ophiopsila cf. polyacantha H. L. Clark, 1915 are described from approximately 15 m water depth at Kakeromajima island, Amami Islands in southwestern Japan. The species occurs on sandy bottoms with the disc buried and the arms extended above the substratum. Bioluminescence and burrowing behavior are described. The specimens are clearly morphologically different from the two species of Ophiopsila Forbes, 1843 previously recorded from Japan. The new Japanese name “Kin-habu-toranoo-kumohitode” is proposed. Key Words: brittle star, scuba diving, bioluminescence, Amami islands, Pacific Ocean. these, only O. pantherina Koehler, 1898 and O. squamifera Introduction Murakami, 1963 have been reported from Japanese waters (Okanishi 2016). Recently, Okanishi et al. (2019) described Recent investigations by SCUBA diving have revealed O. xmasilluminans Okanishi, Oba, and Fujita, 2019 from a many undescribed benthic invertebrate species from the submarine cave in northwestern Australia, with notes on its subtidal zone, usually in depths greater than 10 m, espe- bioluminescence and its sand-burrowing behavior. Howev- cially in the Ryukyu Islands, southwestern Japan (e.g., Kise er, other species with this combination of ecological propen- et al. 2017; Naruse and Yoshida 2018). In this area, many sities have not yet been described from this genus. new records and species of marine benthos from depths Recent descriptions of ophiuroids have included a com- of 15–40 m have recently been described (e.g., Obuchi et prehensive range of photographs and/or drawings of rel- al. 2009; White and Reimer 2012; Fujii and Reimer 2016; evant diagnostic morphological characters as well as scan- Lau et al. 2019). In contrast, benthic fauna of the Amami- ning electron microscope (SEM) images of ossicles, which oshima island which is the second-biggest island within the provide a consistent suite of characters for comparison and Ryukyu Islands, and neighboring Kakeromajima, Ukejima identification (e.g., Martynov 2010; Thuy and Stöhr 2016; and Yorojima islands (in this study, these four islands are Okanishi and Fujita 2018a). Compilation of such data for referred “Amami-oshima island group”; Fig. 1), has been Ophiopsila has only recently begun (e.g., Okanishi et al. poorly studied (e.g., Toyama 2014; Nakae et al. 2018; Reimer 2019). Here, we present detailed photographs of all relevant et al. 2019). Amami-oshima island lies in the northernmost parts of the body for the new recorded species of Ophiopsila area of well-developed coral reefs. The sandy substratum cf. polyacantha H. L. Clark, 1915 from Japan. Additionally, adjacent to the coral reef forms a sheltered bay. Faunistic based on in situ observations, we provide photographs of studies in this area are important for gaining a better un- life color, and brief descriptions of bioluminescence and the derstanding of the marine biodiversity, as it lies within the sand-burrowing behavior of this species. northernmost region of tropical marine ecosystem in Japan. Ophiuroids (Echinodermata) contain the largest number of species within the phylum Echinodermata and they in- Materials and Methods habit nearly all marine habitats (Stöhr et al. 2012; Okanishi 2016). Although some ophiuroid species have been reported Two specimens of Ophiopsila cf. polyacantha were collect- from offshore areas of the Amami-oshima island group (e.g., ed and observed in situ by the second author (TF) during Okanishi and Fujita 2009), the subtidal zone has been barely SCUBA diving at Kedomi, Ikomo Bay, central Kakeroma- explored. jima island, on the southern side of Amami-oshima island, Originally a monotypic genus Ophiopsila Forbes, 1843 Kagoshima [28.097783N, 129.241322E (decimal scale)], (Ophintegrida: Amphilepidida: Ophiopsilidae) currently southwestern Japan, at 15 m depth, on 26 September 2019 comprises 28 nominal species (Okanishi et al. 2019). Of and at 16.7 m depth, on 4 February 2020 (Fig. 1). © 2020 The Japanese Society of Systematic Zoology 284 M. Okanishi and T. Fujii Christodoulou et al. (2019). Taxonomy Class Ophiuroidea Gray, 1840 Superorder Ophintegrida O’Hara, Hugall, Thuy, Stöhr, and Martynov, 2017 Order Amphilepidida O’Hara, Hugall, Thuy, Stöhr, and Martynov, 2017 Suborder Ophiopsilina Matsumoto, 1915 Superfamily Ophiopsiloidea Matsumoto, 1915 Family Ophiopsilidae Matsumoto, 1915 Genus Ophiopsila Forbes, 1843 [New standard Japanese genus name: Toranoo-kumohitode- zoku] Ophiopsila cf. polyacantha H. L. Clark, 1915 [New standard Japanese name: Kin-habu-toranoo-kumo hitode] (Figs 2–8) Ophiopsila polyacantha H. L. Clark, 1915: 297, 298, pl. 14, figs 6, 7; H. L. Clark 1918: 329; Koehler 1930: 209. Material examined. NSMT E-13189: one specimen, Ke- domi, Kakeromajima island, Amami-oshima island, Kago- shima Prefecture, southwestern Japan, depth approximately 15 m, SCUBA diving, collected by T. Fujii, 26 Septem- ber 2019. NSMT E-13190: one specimen, same locality as NSMT E-13189, 16.7 m, 4 February 2020. Fig. 1. Sampling location of Ophiopsila cf. polyacantha (star sym- Diagnosis. Disc surface entirely covered by thick skin; bol). two flat oral papillae s.l.; oral shields oval, longer than wide; dorsal arm plates hexagonal in proximal portion of arms; A single specimen (NSMT E-13189) was anaesthetized in arm spines long and flat, no more than 11 in number on a 10% aqueous solution of magnesium chloride, then fixed proximal portion of arm; adradial tentacle scale narrow and in 99% ethanol. Another single specimen (NSMT E-13190) long; arms approximately 18 times longer than disc diam- was directly immersed in 99% ethanol without anesthetiza- eter; vertebrae with perforation on distal portion of arm. tion. Photographs were taken during anaesthetisation to Description of external morphology (NSMT E-13189). prevent long arms from winding vertically, and fixation of Disc. Circular, 14.3 mm in diameter (Figs 2C–F, 3A), surfac- NSMT E-13189. An arm of NSMT E-13189 was dissected es completely covered by thick skin, and no external ossicles to remove internal ossicles using domestic bleach (ap- observed even when dried (Fig. 3A–C). Radial shields and proximately 5% sodium hypochlorite solution), washed in their surrounds slightly tumid, bar-like, 6 to 7 times longer deionised water, dried in air and mounted on SEM stubs than wide, one third to half disc radius (Fig. 3C). On ven- using double-sided conductive tape. The preparations were tral surface, oral shields, adoral shields and oral plates com- sputter-coated with gold-palladium, examined and photo- pletely covered by the thick skin (Fig. 3D). Oral shield serv- graphed with a Jeol JSM 5510LV SEM of the Misaki Marine ing as madreporite unrecognizable in external view (Fig. Biological Station of The University of Tokyo (MMBS). Both 3D). Interradial ventral disc covered also by skin (Fig. 3E). specimens were deposited in the National Museum of Na- Genital slits long, almost extending to dorsal disc edge (Fig. ture and Science (NSMT). Morphological terminology used 3E, F), approximately 0.27 mm in width (Fig. 3E). Two flat, in this study follows Stöhr et al. (2012), Okanishi and Fujita subequal presumably infradental papillae and adoral shield (2018b), and Hendler (2018). Terminologies of oral papillae spines and a spiniform oral plate ridge papilla just below the were used as sensu lato (hereafter s.l.) in Hendler (2018) and inner presumably infradental papilla at each opening for were mainly determined based on ontogenetic and anatomi- the second tentacle of adoral shield (Fig. 3D). More than 20 cal observations. In this study, we did not observe any on- pointed tooth papillae on dental plate, forming 3 or 4 verti- togenetic series and did not dissect mouth ossicles to pre- cal rows (Fig. 3D). Second tentacle pore completely inside vent destruction of discs of the specimens. Thus, we marked the mouth slit. “?” for these ossicles which we are not sure (Fig. 3D). Sys- Arms. Five, approximately 255 mm long, approximately tematics used in this study follows O’Hara et al. (2018) and 3.3 mm wide and 3.4 mm high in proximal portion, square New record of Ophiopsila cf. polyacantha from Japan 285 Fig. 2. Ophiopsila cf. polyacantha, living, in situ (A, B), anesthetized (C, D) and fixed (E–H) states of a smaller specimen (A, G, H; NSMT E-13190) and a larger specimen (B–F; NSMT E-13189). A, with burrowed disc and extended arms; B, exposed from sand ground, dorsal view; C, E, G, dorsal views; D, F, H, ventral views. Scale bars=1 cm. in cross section. Arms gradually tapering distally (Fig. 2C, External shape of lateral arm plates mostly concealed by D). arm spines, separated by dorsal and ventral arm plates On proximal to middle portion of the arms, ventral arm (Figs 3F, G, 4A, B; see detailed morphological description plates slightly wider than long, distal and proximal sides below). On distal portion of arms, ventral arm plates long, straight and both lateral sides concave, contiguous (Figs 3F, concave on both lateral and distal sides, convex on proximal G, 8M–P). Dorsal arm plates oblong, slightly wider than side (Figs 4H, 8Q, R). Dorsal arm plates longer than wide, long, distal edge slightly rounded, contiguous (Fig. 8G–J). oval, and pointed proximally (Figs 4C, 8K, L). Lateral arm 286 M. Okanishi and T. Fujii Fig. 3. Ophiopsila cf. polyacantha (NSMT E-13189): A, dorsal disc; B, dorsal central part of disc; C, dorsal peripheral part of disc, arrow- heads indicate internal edges of radial shields; D, jaws; E, lateral interradial part of disc; F–H, oral views of arms, proximal (F), middle (G) and distal (H) portions.