Fist Record of Pyatakovestia Boninensis from Ototojima Island, the Bonin Islands, Japan (Arthropoda: Crustacea: Amphipoda) Ko TO

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Fist record of Pyatakovestia boninensis from Ototojima Island, the Bonin Islands, Japan (Arthropoda: Crustacea: Amphipoda)

Ko TOMIKAWA1 and Satoshi SHIMANO2, 3* **

1Department of Science Education, Graduate School of Education, Hiroshima University, Higashi-Hiroshima, 739-8524 Japan 2Science Research Center, Hosei University, 2-17-1, Fujimi, Chiyoda-ku, Tokyo, 102-8160 Japan 3Department of Biological Sciences, Graduate School of Science and Engineering Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji-shi, Tokyo, 192-0397 Japan *Author for correspondence: E-mail [email protected], Tel +81-3-3264-4142, Fax +81-3-3264-4143 **Visiting researcher of Tokyo Metropolitan University

Abstract: Pyatakovestia boninensis Morino and Miyamoto, 2015 is reported based on single female specimen from Ototojima Island, the Bonin Islands, Japan. This is the first record of the species in Ototojima Island. The specimen referred to P. boninensis differs from the original description (type locality: Hahajima Island) by the shape of coxal gill of pereopod 6 and the number of marginal setae of outer ramus of uropod 2.

Keywords: Talitridae, taxonomy, variation

Introduction

Talitrid amphipods occur in various terrestrial environments such as sandy beach, coastal and inland forests, and marshy, which are distributed worldwide. To date, about 250 species have been described in the world (Serejo and Lowry 2008). In Japan, 22 species of 14 genera have been recorded, including an undescribed species (Morino and Miyamoto 2016; Tomikawa 2017). Pyatakovestia boninensis Morino and Miyamoto, 2015 is endemic to the Bonin

− 15 − Islands, which inhabits under wrack in beaches and litter in inland forests (Morino 1991a, b; Morino and Miyamoto 2015; Watanabe 2017). This species was first recorded from Hahajima Island which is the second largest island of the Bonin Islands as an undescribed species of the genus Paciforchestia Bousfield, 1982 (Morino 1991a). Recently, a new genus Pyatakovestia has been established by Morino and Miyamoto (2015), and the undescribed species of Hahajima Island was described and named as a member of Pyatakovestia, with another new species P. iwasai from Honshu, Shikoku, Kyushu, and islands in Nansei Archipelago, Japan. Subsequently, P. boninensis was recorded from Chichijima Island which is the largest island of the Bonin Islands (Watanabe 2017). In 2015, the second author (SS) investigated terrestrial invertebrates of the Bonin Islands. During his samplings, an unidentified amphipod specimen was collected from Ototojima Island which is located in 5 km north of Chichijima Island. After careful examination of these taken amphipods by the first author (KT), one specimen of them is revealed that it belongs to P. boninensis (Tomikawa and Shimano, 2018). In this paper, we report P. boninensis as the first record of the species with taxonomical remarks from Ototojima Island.

Materials and Methods

Amphipods were collected from under litter by hand and fixed in 99% ethanol at the site. Some appendages of the examined specimens of the species were dissected in 99% ethanol and mounted in gum-chloral medium on glass slides under a stereomicroscope (Olympus SZX7). Specimens were examined using a light microscope (Nikon Eclipse Ni) and illustrated with the aid of a camera lucida. The body length from the tip of the rostrum to the base of the telson was measured along the dorsal curvature to the nearest 0.1 mm. The specimen examined is deposited in the Zoological Collection of Kyoto University Fig. 1 Pyatakovestia boninensis, female 8.8 mm, KUZ (KUZ). Z2057, lateral view.

− 16 − Systematics

Pyatakovestia boninensis Morino and Miyamoto, 2015 (Japanese name: Ogasawara-hosohamatobimushi) Figs 1–2

Pyatakovestia boninensis Morino and Miyamoto, 2015: 118, figs. 8–10; Watanabe 2017 67, fig. 4. Paciforchestia sp. 1 Morino 1991a: 65; Morino 1991b 232; Morino 2015 1080, fig. 1.

Material examined. 1 female, 8.8 mm, KUZ Z2057, Tonbo Pond (27.182429°N, 142.188932°E, elevation 14 m; Photograph in Tomikawa and Shimano, 2018), near Mt Hirone, Ototojima Island, the Bonin Islands, Tokyo, Japan, collected by S. Shimano, 28 February 2015.

Diagnosis. Coxal gill of pereopod 6 ovate; surface slightly balbous (Fig. 2A). Uropod 1 (Fig. 2B) with inner and outer rami; inner ramus with 5 dorsomarginal robust setae; outer ramus marginally bare. Uropod 2 (Fig. 2C) with inner and outer rami; inner ramus with 4 dorsomarginal and 4 outer marginal robust setae; outer ramus 3 dorsomarginal robust setae.

Distribution. Hahajima Island (Morino 1991a, b; Morino and Miyamoto 2015), Chichijima Island (Watanabe 2017), and Ototojima Island (present study).

Remarks. Pyatakovestia boninensis is most similar to P. iwasai in having marginally bare outer ramus of uropod 1, smoothly attenuate dactyli of pereopods 3–5 without dorsal fine setae, and ventral margin of anterior lobe on Fig. 2 Pyatakovestia boninensis, female 8.8 mm, KUZ Z2057. A, coxal gill of pereopod 6, medial view; B, right coxa of pereopod 5 with some uropod 1, dorsolateral view; C, right uropod 2, setae. However, the former species dorsomedial view.

− 17 − is distinguished from the latter in having the following features (features of P. iwasai in parentheses): surface of coxal gill of pereopod 6 slightly balbous (smooth); and inner ramus of uropod 2 with 4–6 (3–4) dorsomarginal and 3–5 (1–2) outer marginal robust setae. The present material differs from the holotype of P. boninensis by the following features (features of the holotype in parentheses): coxal gill of pereopod 6 ovate (convoluted); inner ramus of uropod 1 without setae on outer margin (with 2 robust setae); inner and outer rami of uropod 2 with 4 (6) dorsomarginal and 3 (6) marginal robust setae, respectively. Morino and Miyamoto (2015) reported the following variation of uropods 1 and 2: some paratype specimens lack outer marginal setae of inner ramus; inner ramus of uropod 2 with 4–6 dorsomarginal robust setae; and outer ramus of uropod 2 with 5–6 marginal robust setae. The differences between the present material and the holotype seem to represent intraspecific variations, because the setal number of uropods 1 and 2 of the present material is within the variation of P. boninensis reported by Morino and Miyamoto (2015), except the number of marginal setae of outer ramus of uropod 2. The shape of coxal gill of pereopod 6 is however different between the present material and the holotype. Since we could examine single female specimen, additional materials are needed to clarify the inter-variation of the population in morphology among the island. As mentioned above, previously P. boninensis has been recorded from the two largest islands of the Bonin Islands, Chichijima Island and Hahajima Island (Morino 1991a, b; Morino and Miyamoto 2015; Watanabe 2017). The finding of P. boninensis from Ototojima Island may suggest a possibility that the species is also distributed in other small islands of the Bonin Islands. On the other hand, terrestrial invertebrates, especially amphipods and isopods, in Chichijima Island and Hahajima Island have been heavily damaged by an alien nemertine species, Geonemertes pelanensis (Shinobe et al. 2017). From the viewpoint of conservation, an intensive survey of P. boninensis in small islands is a pressing issue.

Acknowledgements This study was financially supported by JSPS KAKENHI Grant Numbers JP17K15174 and JP17H00820.

− 18 − References

Morino H (1991a) Amphipoda. In: Aoki J (ed) Pictorial Keys to Soil Animals of Japan. Tokaidai University Press, Hadano, pp 65–66, figs 213–219. (In Japanese) Morino H (1991b) Talitridae from Ogasawara Islands. Secondary Status Report of Natural Environment of Ogasawara Islands. In: Ogasawara Research Committee (ed) Tokyo Metropolitan University, Tokyo, pp 231–235 (In Japanese) Morino H (2015) Amphipoda. In: Aoki J (ed) Pictorial Keys to Soil Animals of Japan, 2nd ed. Tokaidai University Press, Hadano, pp 1069–1089 (In Japanese) Morino H, Miyamoto H (2015) Redefinition of Paciforchestia Bousfield, 1982 and description of Pyatakovestia gen. nov. (Crustacea, Amphipoda, Talitridae). Bull Nat Mus Nat Sci Ser A 41:105–121. Morino H, Miyamoto H (2016) A new Talitrid genus and species, Lowryella wadai, from estuarine reed mashes of western Japan (Crustacea: Amphipoda: Talitridae). Spec Div 21: 143–149. Serejo CS, Lowry JK (2008) The coastal Talitridae (Amphipoda: Talitroidea) of Southern and Western Australia, with comments on Platorchestia platensis (Krøyer, 1845). Rec Aus Mus 60:161–206. Tomikawa K (2017) Species diversity and phylogeny of freshwater and terrestrial gammaridean amphipods (Crustacea) in Japan. In: Motokawa M, Kajihara H (eds) Species Diversity of Animals in Japan, Diversity and Commonality in Animals. Springer, Tokyo, pp 249–266 doi: 10.1007/978-4-431-56432-4_9 Tomikawa K, Shimano S (2017) Preliminary report: Fist record of Pyatakovestia boninensis from Ototojima Island, the Bonin Islands, Japan (Arthropoda: Crustacea: Amphipoda). Annu Rep Ogasawara Res 41:149–140. (In Japanese)

− 19 − Abstract in Japanese

オガサワラホソハマトビムシの弟島からの初記録（節足動物門：甲殻亜門：端脚目）

富川光 1・島野智之 2* **

1 広島大学大学院教育学研究科 2 法政大学自然科学センター *責任著者 **客員研究員，首都大学東京

小笠原諸島弟島からハマトビムシ科のオガサワラホソハマトビムシを初めて記録した。弟島から得られた雌 1 個体について分類学的検討を行った結果、原記載とは第 6 胸肢の底節鰓の形状、および第 2 尾肢外肢縁棘数について変異がみられることが分かった。

キーワード：ハマトビムシ科、分類、変異

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