Biogeography 22. 58–60. Sep. 20, 2020 The Northernmost Distribution Record of Pentaceraster alveolatus (Echinodermata, Asteroidea) from Sagami Bay, Japan Hisanori Kohtsuka 1*, Hirokazu Yamada 2, Kazuhiko Yamada 2 and Yoichi Kogure 3 1 Misaki Marine Biological Station, The University of Tokyo, 1024 Koajiro, Misaki, Miura, Kanagawa 851-0121, Japan 2 Kannonzaki Nature Museum, 4-1120 Kamoi, Yokosuka, Kanagawa 239-0813, Japan 3 Japan Sea National Fisheries Research Institute, Japan Fisheries Research and Education Agency, 1-5939-22 Suido, Chuo, Niigata, Niigata 951-8121, Japan Abstract: A single specimen of an oreasterid sea star Pentaceraster alveolatus (Perrier, 1875) was collected from the shallow water of Sagami Bay, Kanagawa Prefecture, Japan in May 2019. This specimen is the new distributional and northernmost record of P. alveolatus which so far has been known from the tropical and subtropical waters south of the Kii Peninsula, Wakayama Prefecture. We described the new locality and external features of this sea star that is rarely encountered species in middle latitudinal warm-water settings in Japan. Key words: Pentaceraster alveolatus, Asteroidea, Sagami Bay, northernmost record Introduction Pentaceraster alveolatus: Döderlein, 1916: p. 428, Figs K, L; Fisher, 1919: p. 348, Pl. 101, Fig. 1; A. M. Clark & Rowe, An oreasterid sea star Pentaceraster alveolatus (Perrier, 1971: 34, p. 56; A. M. Clark, 1993: 310. 1875) is distributed in the west Pacific region including New Material examined. OMNH-Iv 8418, inlet under the Jogashi- Caledonia, Melanesia, Indonesia, the Philippines (A. M. ma Ohashi Bridge in Jogasima, Misaki, Miura-city, Kanagawa Clark, 1993), and southern Japan (Saba et al., 2002). In Japa- prefecture, Japan, subtidal zone, skin diving, May 17, 2019, nese waters, this sea star has been recorded along the Pacific collected by Hirokazu Yamada. The living specimen was coast influenced by the warm Kuroshiro Current, such as main reared in the tank at Misaki Marine Biological Station until island of Okinawa, Yaku Island (Saba et al., 2002), and the September 27, 2019. Kii Peninsula that is the known northern limit of occurrence Description. Disc relatively large. Five arms (Fig. 1A, B). (Kubota, 2016; Kubota et al., 2007). Ratio between radial length (R: 97 mm) and interbrachial dis- In May 2019, a single specimen of P. alveolatus was col- tance (r: 37 mm) approximates to 2.6. Breadth of arm approx- lected from the subtidal zone of Sagami Bay at Jogashima, imately 40 mm at arm base. Flat actinal and raised abactinal Misaki, Kanagawa Prefecture, which indicates the noteworthy side; height of center of disk 35 mm. northward range extension of this species. In this paper, we Five large hemispherical spines on center of abactinal disk describe the locality and external features of this sea star based (Fig. 1C); seven to nine relatively large hemispherical spines on the specimen representing a new northern limit of the dis- in carinal plate with a few smaller spines interspersed between tribution for P. alveolatus in Japan. them (Fig. 1D). Two rows of spines on each side of carinal The specimen used in this report are immersion specimens plate; a small number of spines in outer row. fixed in 99% ethanol aqueous solution, deposited in Osaka A large number of conspicuous white papulae in gaps be- Museum of Natural History (OMNH). tween each spine, clearly delineating papular area. Madrepo- rite triangle with rounded corners in shape, approximately 5 mm in length, situated in interbrachial area: 15 mm away from Pentaceraster alveolatus (Perrier, 1875) center of disk. Bivalve shaped pedicellariae on side of mouth Japanese name: Kobuhitode-modoki (Fig. 1E). (Fig. 1) Outer part of disk edged by marginal plates; each supero- marginal and the inferomarginal plate having prominent bulge Pentaceros alveolatus Perrier, 1875: p. 243. (Fig. 1F). Adambulacral plate contains 5-7 furrow spines and −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− two rows of 2-4 and 2-3 thicker and shorter subambulacral *Corresponding author: [email protected] spines, respectively (Fig. 1G). – 58 – Hisanori Kohtsuka, Hirokazu Yamada, Kazuhiko Yamada and Yoichi Kogure Fig. 1. Pentaceraster alveolatus of living specimen (OMNH-Iv 8418). A: abactinal view. B: actinal view. C: abactinal view of central body; white arrow indicating a madreporite. D: abactinal view of arm. E: mouth plates; black arrows indicating pedicellariae. F: side view of arm tip. G: adambu- lacral spines; f: furrow spines, s: subambulacral spines. Scale bars: A, B = 30 mm; C, D, F = 10 mm; E, G = 5 mm. Color in life. Abactinal surface grayish-green. Tip of the 2002). arm and disk margin brown. Conspicuous hemispherical spine The present specimen was identified as Pentaceraster alve- yellow. Area among the spines without papula greenish brown. olatus (Perrier, 1875) based on the external features: R/r of 2.6, Actinal surface generally grayish-white, with the exception of five large hemispherical spines on the center of the abactinal pale purple central mouth area. side, relatively large spines on the carinal plates, a well-divid- Remarks. The sea star belonging to Oreasteridae has stel- ed papular area, and the structure of the adambulacral spines. late, pentagonal, or rarely spherical body, the surface of which These external features are consistent with those described by is often covered with thick skin having granules. The disk is Fisher (1919). large with raised abactinal and flattened actinal side. Most of The type locality of this species is New Caledonia (Perrier, the species have huge cone-shaped hump and spines on the 1875). Other specimens were known from shallow waters at abactinal side. The abactinal skeleton is composed of large, depth of 1-54 m in Australia, Melanesia, Indonesia, the Philip- reticulated plates, which forms wide papular area (Saba et al., pines, southern China, the main island of Okinawa, and Yak- – 59 – Pentaceraster alveolatus from Sagami Bay ushima Island of Kagoshima Prefecture (A. M. Clark, 1993; Kogure, Y., 2018. A checklist of sea stars (Echinodermata, Liao & A. M. Clark, 1995; Rowe & Gates, 1995; Saba et al., Asteroidea) from Japanese waters. Bulletin of the Biogeo- 2002). More recently, several specimens were obtained at Shi- graphical Society of Japan, 73: 70–86. (in Japanese with rahama, Wakayama Prefecture (Kubota, 2016; Kubota et al., English abstract) 2007). This report is the northernmost record of this sea star, Liao, Y. & Clark, A. M., 1995. The Echinoderms of southern as well as the new locality in Japan. China. 614 pp. Science Press, Beijing. Concerning the taxonomy of Pentaceraster sea stars, Mah, C. L., 2019. World Asteroidea database. Available online Döderlein (1936) pointed out that it is difficult to distinguish at http: // www. marinespecies. Org / aphia. php?p = taxde- P. alveolatus (Perrier, 1875) from P. multispinus (von Mar- tails&id = 370898 on 2019-07-21 tens, 1866). Furthermore, A. M. Clark & Rowe (1971) found Perrier, E., 1875. Revision de la collection de Stellérides du it difficult to distinguish P. alveolatus from P. regulus (Müller Muséum d’ Histoire Naturelle de Paris, 84 pp. Paris. & Troschel, 1842). The genus Pentaceraster is a group that Rowe, F. W. E. & Gates, J., 1995. Zoological Catalogue of needs to be reviewed taxonomically; it is desirable to organize Australia. Echinodermata. 510 pp. CSIRO Australia, Mel- the species classification based on both the traditional mor- bourne. phology and molecular phylogeny. Saba, M., Irimura, S., and Soyama, I., 2002. Sea Stars and Brittle Stars in Japanese Waters. 135 pp., TBS Britannica, Acknowledgements Tokyo. (in Japanese) We would like to thank Dr. Masanori Okanishi of Misaki (Received June 17, 2020; Accepted July 21, 2020) Marine Biological Station, the University of Tokyo, for his review, and Dr. So Ishida of the Osaka Museum of Natural History for his cooperation in the registration of the speci- mens. We extend our gratitude to the reviewers for their useful suggestions. References Clark, A. M., 1993. An index of names of recent Asteroidea Part 2: Valvatida. In Jangoux, M. and Lawrence, J. M. (Eds), Echinoderm Studies, 4: 187–366. A. A. Balkema, Rotter- dam. Clark, A. M. & Rowe, F. W. E., 1971. Monograph of shal- low-water Indo-West Pacific echinoderms. Trusties of the British Museum of Natural History London, 238 pp, 31 pls. Döderlein, L., 1916. Uber die Gattung Oreaster und verwan- dte. Zoologische Jahrbücher, 40: 409–440. Fisher, W. K., 1919. Starfishes of the Philippine seas and adja- cent waters. Bulletin of the United States National Museum, 100 (3): 1–547. Kubota, S., 2016. Reappearance of a living, small individual of Pentaceraster alveolatus (Asteroidea; Oreasteridae) at “Kitahama” beach of the Seto Marine Biological Laborato- ry, Kyoto University, Shirahama Town, Wakayama Prefec- ture, Japan. Nankiseibutu, 58 (2): 224–225. (in Japanese) Kubota, S., Kashiyama, Y. & Tanase, H., 2007. Pentaceraster alveolatus (Asteroidea; Oreasteridae) washed ashore at Banshozaki and Kitahama beach of the Seto Marine Bio- logical Laboratory, Kyoto University in Shirahama Town, Wakayama Prefecture, Japan. Journal of Japan Driftologi- cal Society, 5: 45–46. – 60 –.