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INTRODUCTION

Apseudes nipponicus SHIINO, 1937 is the first described tanaidacean species in Japan (KAKUI, 2016). In Tanaidacea, most members of which are approximately a few millimeters in length (LARSEN et al., 2015), A. nipponicus is a relatively large-sized species, reaching 16 mm in length (SHIINO, 1937). This species has a digging-type pereopod 1 (cf. LARSEN et al., 2015), suggesting its burrowing mode of life. SHIINO (1937) described A. nipponicus based on specimens collected from a mud bottom at a depth of 13 m in Sagami Bay (off Hayama, Kanagawa), and also included data from several specimens from the Sagami Sea (Nabeta, Shizuoka).　　Sagami Bay and the Sagami Sea are the best studied marine areas in Japan (KAJIHARA & KAKUI, 2016). For about 40 years since the 1930s, HIROHITO, the Emperor Showa, had conducted faunal surveys of the area (A. nipponicus was described based on specimens collected during this survey). In recent years, JAMBIO, the Japanese Association for Marine Biology, has hosted a serial survey and actively investigated marine fauna around the Shimoda Marine Research Center (SMRC) of the University of Tsukuba, and the Misaki Marine Biological Station (MMBS) of the University of Tokyo, by

using grab-samplers, dredges, and sledge-nets (NAKANO et al., 2015). Thus far, nine surveys incorporating 59 sampling sites, ranging from 2 to 750 m in depth, have been conducted (NAKANO et al., 2015; JAMBIO, 2016).

Despite the large body size of this species and the great sampling efforts in Sagami Bay and the Sagami Sea, after SHIINO’ s (1937) original description, additional reports of A. nipponicus were very limited. The only published record is an illustrated encyclopedia (OKUTANI, 1994), which presented a photo of a live individual collected from a muddy bottom in shallow water around Hayama. A recent serial survey by JAMBIO around SMRC and MMBS col lected many tanaidaceans but failed to obtain any specimen of this species (K. KAKUI, unpublished data). In 2014, we discovered several individuals of A. nipponicus for the first time in decades, and also collected this species in 2015 and 2016. In this study, in addition to observations of living animals, we discuss the preferred habitat of this species.

MATERIALS AND METHODS

Sampling was performed at the SMRC on 16 May 2014 and 7 April 2015. The bottom substrates in experimental

aquaria for rearing a colonial ascidian Didemnum vexillum (in 2014) or a gastropod Strombus luhuanus (in 2015) were collected by a siphon and then filtered by a hand net, and tanaidaceans were picked up from the residue. Individuals found in 2014 were released into the sea after taking photos. Fifty specimens collected in 2015 were fixed by ethanol or formalin, about 140 tanaidaceans were sent live to KK’s lab at Hokkaido University and used to observe their burrowing behavior, while others were released into the sea. A scuba sampling around MMBS was carried out on 25 May 2016. The sampling site was at a depth of 2 m around a small pier for MMBS’s research boat (35° 9′ 27.507″ N, 139° 36′ 43.704″ E). Collected specimens were fixed in ethanol. Two fixed specimens collected from SMRC were deposited in the Kitakyushu Museum of Natural History & Human History (KMNH IvR 500921). In all samplings, the accompanying fauna was not checked.

Living individuals of A. nipponicus were kept at room temperature and under ambient light in the laboratory. As muddy sand substrates where our specimens were collected could not be prepared, and one congener (Apseudes sp.) has been successfully maintained in coral sand for years (KAKUI & HIRUTA, 2013), three size categories of coral sand (> 1 mm, 1–0.5 mm, and 0.5–0.3 mm in diameter; about 1,400 g/l) were used as bottom substrates. We also tested commercial aquarium gravel, Pure Black (JAN code 4972547010049, GEX, Japan; 2–4 mm in grain size, 750 g/l), as a bottom substrate. The behavior of animals was observed with the naked eye.

RESULTS AND DISCUSSION

In SMRC, A. nipponicus (Fig. 1A) was collected from a muddy sand bottom in experimental aquaria. This is the first record from an artificial environment for this species. A few specimens were found in 2014, and numerous (more than 190) individuals were collected in 2015. How they colonized the aquaria remains unclear. One possibility is that tanaidaceans were attached to the surface of colonial ascidians or gastropods when these were placed into the aquaria. Another possible route by which A. nipponicus may have entered the aquaria is via the intake hosepipe of sea-water which is placed near the sea-bottom at a sea depth of 3 m in front of the SMRC, at Nabeta Bay, where some of the type specimens were collected (SHIINO, 1937). As our sample included individuals of various sizes, some of which were ovigerous, A. nipponicus appears to reproduce in these aquaria. The bottom sand in the aquaria was black, indicating that it contains sulfide. Around MMBS, three specimens were collected. All specimens were found under fist-sized rocks partly buried in mud (Fig. 1B). This is the first in-situ observation of this species in a natural environment. The substrate under the rocks was blackish, sulfide-containing muddy sand.　　Rearing experiments showed that A. nipponicus could

burrow the artificial substrate covered by Pure Black (aquari-um gravel) but not coral sand, suggesting that there are usable and unusable bottom conditions for A. nipponicus. Incidenta-lly, a congener Apseudes sp. sensu KAKUI & HIRUTA (2013) was able to burrow into Pure Black as well as into coral sand (KAKUI & HIRUTA, 2013; K. KAKUI, unpublished data). This is the first evidence of differences in the burrowing ability among congeneric species.　　In Tanaidacea, the habitat preference of species is poorly understood. For species that were repeatedly collected from some specialized environments, their habitat preference has been suggested, such as the surface of sea turtles or manatees for some Hexapleomera species (MORALES-VELA et al., 2008; BAMBER, 2012), the inside of the body wall of deep-sea holothurians for Exspina typica LANG, 1968 (ALVARO et al., 2011), and deep-sea sunken woods for members of Protanais (MCCLAIN & BARRY, 2014; BŁAŻEWICZ-PASZKOWYCZ et al., 2015). BŁAŻEWICZ-PASZKOWYCZ et al. (2011) proposed that the genera Cristatotanais, Coalecerotanais, and Obesutanais supposedly are associated with and adopted to chemically-reduced habitats like mud-volcanoes, cold seeps, and hydrothermal vents. For A. nipponicus, SHIINO (1937, p. 60) presented a postscript about the environment where specimens were collected: “They were found from a well-like pit 13 m deep artificially (?) excavated on a reef [ … ] The bottom of the

deep pit, inhabited gregariously by this animal, is covered with mud which has the smell of hydrogen sulphide.” Both habitats around SMRC and MMBS, where our specimens were found, were a less-disturbed, sulfide-containing muddy sand bottom, roughly corresponding to that noted by SHIINO (1937). In add-ition, our observation of living A. nipponicus indicated that its habitat is restricted by the type of bottom substrate. Consider-ing SHIINO (1937) and our present results, A. nipponicus likely prefers (or may be confined to) a less-disturbed, sulfide-conta-ining muddy sand bottom. This probable specialized habitat may be one reason why so few records exist for this species.

ACKNOWLEDGMENTS

We thank Yasutaka TSUCHIYA, Toshihiko SATO, Hideo SHINAGAWA, Yutaro YAMADA, and Daisuke SHIBATA for help in collecting the tanaidaceans from experimental aquaria in SMRC; Morihiko TOMATSURI for help in sending live specimens collected in 2015; and Mamoru SEKIFUJI for help in sampling around MMBS in 2016.

REFERENCES

ALVARO, M. C., BŁAŻEWICZ-PASZKOWYCZ, M., DAVEY, N. & SCHIAPARELLI, S. 2011. Skin-digging tanaids: the unusual parasitic behavior of Exspina typica in Antarctic waters and worldwide deep basins. Antarctic Science, 23: 343–348.

BAMBER, R. N. 2012. A re-assessment of Hexapleomera DUDICH, 1931 (Crustacea: Tanaidacea: Tanaidae), with designation of three new species. Zootaxa, 3583: 51–70.

BŁAŻEWICZ-PASZKOWYCZ, M., BAMBER, R. N. & CUNHA, M. R. 2011. New tanaidomorph Tanaidacea (Crustacea: Peracarida) from submarine mud-volcanoes in the Gulf of Cadis (North-east Atlantic). Zootaxa, 2769: 1–53.

BŁAŻEWICZ-PASZKOWYCZ, M., KOBYŁECKA, E. & JENNINGS, R. N. 2015. Redescription of wood-associated tanaidacean Protanais birsteini (KUDINOVA-PASTERNAK, 1970) and its relationship within the Tanaididae. Deep-Sea Research II, 111: 333–342.

JAMBIO. 2016. http://www.shimoda.tsukuba.ac.jp/~jambio/

　　index.html [accessed 6 August 2016]KAJIHARA, H. & KAKUI, K. 2016. An overview of recent

marine-biodiversity research in Japan. In MOTOKAWA, M. & KAJIHARA, H. (eds.) Species Diversity of Animals in Japan, pp. 25–45. Springer, Berlin.

KAKUI, K. 2016. Review of the taxonomy, diversity, ecology, and other biological aspects of Order Tanaidacea from Japan and surrounding waters. In MOTOKAWA, M. & KAJIHARA, H. (eds.) Species Diversity of Animals in Japan, pp. 603–627. Springer, Berlin.

KAKUI, K. & HIRUTA, C. 2013. Selfing in a malacostracan crustacean: why a tanaidacean but not decapods. Naturwissenschaften, 100: 891–894.

LARSEN, K., GUŢU, M. & SIEG, J. 2015. Order Tanaidacea DANA, 1849. In VON VAUPEL KLEIN, J. C., CHARMANTIER-

　　DAURES, M. & SCHRAM, F. R. (eds.) Treatise on Zoology-　　Anatomy, Taxonomy, Biology. The Crustacea 5, pp.

249–329. Brill, Leiden.MCCLAIN, C. & BARRY, J. 2014. Beta-diversity on deep-sea

wood falls reflects gradients in energy availability. Biology Letters, 10: 20140129.

MORALES-VELA, B., SUÁREZ-MORALES, E., PADILLA-SALDÍVAR, J. & HEARD, R. W. 2008. The tanaid Hexapleomera robusta (Crustacea: Peracarida) from the Caribbean manatee, with comments on other crustacean epibionts. Journal of the Marine Biological Association of the United Kingdom, 88: 591–596.

NAKANO, H., KAKUI, K., KAJIHARA, H., SHIMOMURA, M., JIMI, N., TOMIOKA, S., TANAKA, H., YAMASAKI, H., TANAKA, M., IZUMI, T., OKANISHI, M., YAMADA, Y., SHINAGAWA, H., SATO, T., TSUCHIYA, Y., OMORI, A., SEKIFUJI, M. & KOHTSUKA, H. 2015. JAMBIO Coastal Organism Joint Surveys reveals undiscovered biodiversity around Sagami Bay. Regional Studies in Marine Science, 2 supplement: 77–81.

OKUTANI, T. 1994. Yama-Kei Field Books 8. Yama-Kei Publishers, Tokyo, 368 pp. [ In Japanese]

SHIINO, S. M. 1937. On Apseudes nipponicus n. sp. (Crustacea, Tanaidacea). Annotationes Zoologicae Japonenses, 16: 53–62.

Bull. Kitakyushu Mus. Nat. Hist. Hum. Hist., Ser. A, 15: 1–3, March 31, 2017

Habitat of a tanaidacean Apseudes nipponicus SHIINO, 1937

ABSTRACT − Apseudes nipponicus SHIINO, 1937 is the first described tanaidacean species in Japan. This species is a relatively large-sized member among tanaidaceans, reaching 16 mm in length. Its type specimens were collected from shallow water in Sagami Bay and the Sagami Sea, the best-studied marine areas in Japan. Despite the large body size of this species and great sampling efforts in this area, additional published records of this tanaidacean are limited to an illustrated encyclopedia. In this study, we report A. nipponicus from Sagami Bay and the Sagami Sea for the first time in decades. More than 190 individuals were collected from experimental aquaria at the Shimoda Marine Research Center of the University of Tsukuba, where colonial ascidians or gastropods were reared. In aquaria, tanaidaceans inhabited a blackened muddy bottom, and reproduced there. In addition, three animals were collected from another natural environment, a muddy substrate under fist-sized rocks at a depth of 2 m around the Misaki Marine Biological Station of the University of Tokyo. Considering the environments where SHIINO’ s and our samples were collected, A. nipponicus likely prefers less-disturbed, sulfide-containing muddy substrates, and this probable specialized habitat may be one reason why so few records exist for this species.

KEY WORDS: Crustacea, Tanaidacea, Apseudidae, Japan, microhabitat, artificial environment

Keiichi KAKUI 1※, Atsuko SUZUKI2, Hiroaki NAKANO2 & Hisanori KOHTSUKA3

1Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan2Shimoda Marine Research Center, University of Tsukuba, Shimoda 415-0025, Japan3Misaki Marine Biological Station, The University of Tokyo, Miura 238-0225, Japan

※Corresponding author. Email: kakui@eis.hokudai.ac.jp

(Received August 25, 2016; Accepted October 18, 2016)

は　じ　め　に

　サバ目サバ亜目サバ科サワラ族魚類は 3属 21種の現生種が知られており，海水生であるが，河口や 300 km上流のメコン川にも見られる（NELSON et al., 2016）．世界の熱帯から温帯の海域に生息し，サワラ属（Scomberomorus）魚類は東部大西洋に 1種，西部大西洋に 4種，東太平洋に 2種 ,インド－西太平洋に 11 種が分布する（COLLETTE and NAUEN, 1983; COLLETTE and RUSSO, 1985）．ニジョウサバ属（Grammatorcynus）魚類は 2 種が知られており，オーストラリアと北大西洋にそれぞれ分布する．カマスサワラ属（Acanthocybium）は 1 種で熱帯から温帯にかけて汎世界的に分布する（COLLETTE and NAUEN, 1983）．　本邦におけるサワラ族魚類化石は，ニジョウサバ属では尾部骨格が富山市の八尾層群黒瀬谷層（中新統）から報告されている（UYENO and FUJII, 1975）．サワラ属魚類では前上顎骨が岡山県津山市の勝田層群（中新統）から（大江ほか，1986），頭蓋骨，肩帯，肋骨，脊椎骨の一部が埼玉県秩父郡小鹿野町の秩父町層群（中新統）から産出しており（上野・

坂本，1985），石川県金沢市の大桑層（更新統）からも左上顎骨が報告されている（松浦，1996）．また，カマスサワラ属では頭蓋骨が岐阜県瑞浪市から，歯骨が土岐市の瑞浪層群（中新統）から産出している（大江ほか，1981）．国外では主にイギリスや中近東の古第三系などから産出しており（e.g. MONSCH, 2004; MONSCH and BANNIKOV, 2011），例えばサワラ属の化石種である Scomberomorus avitus BANNIKOV, 1985がトルクメニスタンの古第三系上部から，Scomberomo-rus avitus BANNIKOV, 1982 がカザフスタンの始新統から記載されている（BANNIKOV, 1982; 1985）．今回報告する標本は岡山県新見市西部から 1994 年に著者の一人である石垣によって発見されたもので，サバ科サワラ族に属するものと考えられる．なお，骨の部分の名称は須田（1991）に従った．

産地と層序

　岡山県新見市西方付近では基盤岩を不整合に覆って下部中新統の備北層群が分布しており，種々の斧足類，掘足類，腹足類，カメ類などの化石が豊富に産出している（e.g. 田

口ほか，1979；平山ほか，1982；1983；平山・田口，1994）．特に，2000 年ごろまでは新見市西部辻田の旧小野田セメント粘土採掘場跡は化石が豊富に産出することが知られていた．今回報告する化石はこの採泥跡地から発見されたもので，田口ほか（1979）の Loc. 4にあたる（Fig. 1）．田口ほか（2013）によれば化石産地の中新統を上田（1989）の備北層群是松層としていることから本標本は本層の暗灰色泥岩から産出したと考えられる．

記　　載

硬骨魚綱　Osteichthyes HUXLEY, 1880条鰭亜綱　Actinopterygii KLEIN, 1885真骨区　Teleostei MÜLLER 1845

サバ目　Scombriformes (Pelagia) MIYA et al., 2013サバ亜目　Scombroidei BLEEKER, 1859

サバ科　Scombridae RAFINESQUE – SCHMALTZ, 1815サワラ族　Scomberomorini STARKS, 1910カマスサワラ属　Acanthocybium GILL, 1862

Acanthocybium sp.

標本番号　KMNH (Kitakyushu Museum of Natural History and Human History)VP 100,335，左前上顎骨の一部

　本標本は上向突起（ascending process）が発達すること，骨の縁辺に歯が並ぶこと，上向突起の後ろに主上顎骨関節突起（articulation process for maxilla）があることから左前上顎骨と考えられる（Fig. 2）．前部が保存されており，後部は欠損する．上向突起の側面観は矢じり状で，その前縁はほぼ直線的である．上向突起の高さは 36.8 mm で後方へ

の傾きは約 43°である．骨の表面は全体的に磨耗しており，破損しているところもある．内側の関節面等は磨耗により残されていない．外側面は全体に緩やかに膨出するが，下半部は平面的である．　外側面の歯槽部分は骨で覆われているが，内側面の歯槽部分の骨は欠損し，象牙質が露出している．上向突起のすぐ後ろの部分に主上顎骨関節突起の膨らみが残されており，この部分が全体の中でもっとも厚く，厚さは 9.0 mmである．　関節突起より後ろの部分は上部が厚く，下方に向かって薄くなる．内側面は後方に向かうに従って下部が薄くなる．保存されている後部の一番低いところは 17.0 mmである．　歯は全体に磨耗しており，破損しているところもあるが，歯槽部分は象牙質で充填されている．歯のかなりの部分が磨耗しているため，それぞれの歯の境界が明確でないものもあるが，歯の水平断面は丸くなく，側偏し，歯は比較的大きい．また，前方のものほど小さい傾向にある．大きな歯のおおよその幅は 4.3 mmであり，小さな歯の幅はおよそ1.5 mmである．少なくとも 19本が確認できる．

考　　察

　本標本は歯があること，上向突起があることから真骨魚類の前上顎骨と考えられる．上向突起が矢じり状を呈することや残された後部に厚みがあること，関節突起より後方の部分は高さがほぼ一定であることなどからサバ科サワラ族に属するものと考えられる．　サワラ族はニジョウサバ属，サワラ属，カマスサワラ属からなり，サワラ属はカマスサワラ属と 17 の骨学的形質を共有することから姉妹群と考えられている（COLLETTE and RUSSO, 1985）．ニジョウサバ属の前上顎骨の歯の断面は扁

平せず丸いが（Fig. 3），サワラ属とカマスサワラ属では側偏する（Figs. 4, 5）．サワラ属では歯と歯の間は広く空いており，歯槽の中に次の小さな歯が見られる（Fig. 4）が，カマスサワラ属では歯と歯の間は空いていない（Fig. 5）．　本標本は歯が丸くなく，側扁すること，隙間なく並んでいる点ではサバ科サワラ族のカマスサワラ属に類似する（Figs. 2, 5）．本化石の個体は全長 166 cm のカマスサワラの前上顎骨との比較から推定全長はおよそ 140 cm と考えられる．　サワラ属魚類は岡山県津山市の勝田層群から前上顎骨が報告されており（大江ほか，1986），全体的な形状は今回の標本に類似する．しかし，勝田層群産の化石が 歯と歯の間が離れており，次の歯が形成される孔があるといったサワラ属の特徴を示すのに対し，新見産の本標本にはそのような特徴は見られない．また，埼玉県秩父郡小鹿野町の秩父町層群からサワラ属の頭蓋骨，肩帯，肋骨，脊椎骨の一部

が産出しているが，前上顎骨は産出していない（上野・坂本，1985）．　本邦における中新世のカマスサワラ属魚類化石は岐阜県の瑞浪層群から知られており，瑞浪市からは頭蓋骨が，土岐市からは歯骨が報告されているが，前上顎骨は産出していない（大江ほか，1981）．瑞浪層群のカマスサワラ属の歯骨の歯は大きさや並び方で本標本に類似しており，同一種の可能性も考えられる．　現生のカマスサワラ属魚類はカマスサワラ（Acanthocyb-ium solandri (CUVIER, 1829)） 1 種であるが，今回の化石はカマスサワラとは次の点で異なる．(1) 前上顎骨の歯はカマスサワラより大きい，カマスサワラの歯は比較的小さく，後方に向かうに従って次第に大きくなる．(2) 前上顎骨の口縁（下縁）前部は直線的であるが，カマスサワラでは緩やかに湾入する．

(3) 前上顎骨の上向突起前縁の後方への傾きが 43°とカマス 　 サワラに比べて大きく，Scomberomorus lineolatus（23° : DEVARAJ, 1975）を除くサワラ属の範囲内（32–61°: COLLET-TE and RUSSO, 1985）である．カマスサワラでは 34–37° （Co-LLETTE and RUSSO, 1985）であり，傾きがより小さい．　以上のように本種は歯が側扁し隙間なく並んでいることからカマスサワラ属の一員としたが，歯はカマスサワラよ

りも大きく，上向突起の形態ではむしろサワラ属に類似することから新たな属を考える必要があるかもしれない．本種はカマスサワラ属とサワラ属の系統関係やサワラ族魚類の起源と進化に関する知見を得る上で重要な種と考えられ，さらなる標本の産出が期待される．

謝　　辞

　本研究を進めるにあたり，国立科学博物館所蔵の現生骨格標本の観察にご協力いただいた国立科学博物館名誉研究員の上野輝彌博士ならびに標本資料センターディレクター及び分子生物多様性研究資料センター長の真鍋真博士に心より感謝の意を表する．また，水産大学校の須田有輔博士ならびに城西大学の宮田真也博士からは査読者として多くの貴重なコメントをいただいた．ここに記してお礼申し上げる．なお，本研究は JSPS 科研費 JP2640506（籔本）の助成を受けた．

文　　献

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Tasmanicisque. Verhandelingen der Natuurkundige Vereeniging in Nederlandsch Indië, 6: 1–276.

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Illustrated Catalogue of Tunas, Mackerels, Bonitos and Related Species Known to Date. FAO Fisheries Synopsis no 125. vol. 2, 137 pp. Rome: FAO 1983. ISBN-Nr. 92-

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平山廉・田口栄次・岡崎美彦． 1982. 岡山県新見市の中新統備北層群より発見された汽水棲カメ類の第 2 個体． 瑞浪市化石博物館研究報告， (9): 111–116.

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　 idei, Perciformes), including billfishes, from the Cenozoic of territories of the former USSR. Transactions of the Royal Society of Edinburgh. Earth Sciences, 102(04): 253–300.

NELSON, J. S., T. C. GRANDE, and M. V. H. WILSON. 2016. Fishes- 　 of the world. Fifth edition. John Wiley & Sons, Inc., Hobok- 　 en, New Jersey, 752 pp.大江文雄・西本博行・奥村好次・東好昭． 1981. 瑞浪層群産 “カマスサワラ”属魚類化石．瑞浪市化石博物館研究報告， (8): 25–46.

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pp.STARKS, E. C. 1910. The osteology and mutual relationships of

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山崎京美・上野輝彌． 2008. 硬骨魚類の顎と歯． アート＆サイエンス工房　TALAI, 339 pp.

2 Keiichi KAKUI et al. Habitat of Apseudes nipponicus 3

INTRODUCTION

Apseudes nipponicus SHIINO, 1937 is the first described tanaidacean species in Japan (KAKUI, 2016). In Tanaidacea, most members of which are approximately a few millimeters in length (LARSEN et al., 2015), A. nipponicus is a relatively large-sized species, reaching 16 mm in length (SHIINO, 1937). This species has a digging-type pereopod 1 (cf. LARSEN et al., 2015), suggesting its burrowing mode of life. SHIINO (1937) described A. nipponicus based on specimens collected from a mud bottom at a depth of 13 m in Sagami Bay (off Hayama, Kanagawa), and also included data from several specimens from the Sagami Sea (Nabeta, Shizuoka).　　Sagami Bay and the Sagami Sea are the best studied marine areas in Japan (KAJIHARA & KAKUI, 2016). For about 40 years since the 1930s, HIROHITO, the Emperor Showa, had conducted faunal surveys of the area (A. nipponicus was described based on specimens collected during this survey). In recent years, JAMBIO, the Japanese Association for Marine Biology, has hosted a serial survey and actively investigated marine fauna around the Shimoda Marine Research Center (SMRC) of the University of Tsukuba, and the Misaki Marine Biological Station (MMBS) of the University of Tokyo, by

using grab-samplers, dredges, and sledge-nets (NAKANO et al., 2015). Thus far, nine surveys incorporating 59 sampling sites, ranging from 2 to 750 m in depth, have been conducted (NAKANO et al., 2015; JAMBIO, 2016).

Despite the large body size of this species and the great sampling efforts in Sagami Bay and the Sagami Sea, after SHIINO’ s (1937) original description, additional reports of A. nipponicus were very limited. The only published record is an illustrated encyclopedia (OKUTANI, 1994), which presented a photo of a live individual collected from a muddy bottom in shallow water around Hayama. A recent serial survey by JAMBIO around SMRC and MMBS col lected many tanaidaceans but failed to obtain any specimen of this species (K. KAKUI, unpublished data). In 2014, we discovered several individuals of A. nipponicus for the first time in decades, and also collected this species in 2015 and 2016. In this study, in addition to observations of living animals, we discuss the preferred habitat of this species.

MATERIALS AND METHODS

Sampling was performed at the SMRC on 16 May 2014 and 7 April 2015. The bottom substrates in experimental

aquaria for rearing a colonial ascidian Didemnum vexillum (in 2014) or a gastropod Strombus luhuanus (in 2015) were collected by a siphon and then filtered by a hand net, and tanaidaceans were picked up from the residue. Individuals found in 2014 were released into the sea after taking photos. Fifty specimens collected in 2015 were fixed by ethanol or formalin, about 140 tanaidaceans were sent live to KK’s lab at Hokkaido University and used to observe their burrowing behavior, while others were released into the sea. A scuba sampling around MMBS was carried out on 25 May 2016. The sampling site was at a depth of 2 m around a small pier for MMBS’s research boat (35° 9′ 27.507″ N, 139° 36′ 43.704″ E). Collected specimens were fixed in ethanol. Two fixed specimens collected from SMRC were deposited in the Kitakyushu Museum of Natural History & Human History (KMNH IvR 500921). In all samplings, the accompanying fauna was not checked.

Living individuals of A. nipponicus were kept at room temperature and under ambient light in the laboratory. As muddy sand substrates where our specimens were collected could not be prepared, and one congener (Apseudes sp.) has been successfully maintained in coral sand for years (KAKUI & HIRUTA, 2013), three size categories of coral sand (> 1 mm, 1–0.5 mm, and 0.5–0.3 mm in diameter; about 1,400 g/l) were used as bottom substrates. We also tested commercial aquarium gravel, Pure Black (JAN code 4972547010049, GEX, Japan; 2–4 mm in grain size, 750 g/l), as a bottom substrate. The behavior of animals was observed with the naked eye.

RESULTS AND DISCUSSION

In SMRC, A. nipponicus (Fig. 1A) was collected from a muddy sand bottom in experimental aquaria. This is the first record from an artificial environment for this species. A few specimens were found in 2014, and numerous (more than 190) individuals were collected in 2015. How they colonized the aquaria remains unclear. One possibility is that tanaidaceans were attached to the surface of colonial ascidians or gastropods when these were placed into the aquaria. Another possible route by which A. nipponicus may have entered the aquaria is via the intake hosepipe of sea-water which is placed near the sea-bottom at a sea depth of 3 m in front of the SMRC, at Nabeta Bay, where some of the type specimens were collected (SHIINO, 1937). As our sample included individuals of various sizes, some of which were ovigerous, A. nipponicus appears to reproduce in these aquaria. The bottom sand in the aquaria was black, indicating that it contains sulfide. Around MMBS, three specimens were collected. All specimens were found under fist-sized rocks partly buried in mud (Fig. 1B). This is the first in-situ observation of this species in a natural environment. The substrate under the rocks was blackish, sulfide-containing muddy sand.　　Rearing experiments showed that A. nipponicus could

burrow the artificial substrate covered by Pure Black (aquari-um gravel) but not coral sand, suggesting that there are usable and unusable bottom conditions for A. nipponicus. Incidenta-lly, a congener Apseudes sp. sensu KAKUI & HIRUTA (2013) was able to burrow into Pure Black as well as into coral sand (KAKUI & HIRUTA, 2013; K. KAKUI, unpublished data). This is the first evidence of differences in the burrowing ability among congeneric species.　　In Tanaidacea, the habitat preference of species is poorly understood. For species that were repeatedly collected from some specialized environments, their habitat preference has been suggested, such as the surface of sea turtles or manatees for some Hexapleomera species (MORALES-VELA et al., 2008; BAMBER, 2012), the inside of the body wall of deep-sea holothurians for Exspina typica LANG, 1968 (ALVARO et al., 2011), and deep-sea sunken woods for members of Protanais (MCCLAIN & BARRY, 2014; BŁAŻEWICZ-PASZKOWYCZ et al., 2015). BŁAŻEWICZ-PASZKOWYCZ et al. (2011) proposed that the genera Cristatotanais, Coalecerotanais, and Obesutanais supposedly are associated with and adopted to chemically-reduced habitats like mud-volcanoes, cold seeps, and hydrothermal vents. For A. nipponicus, SHIINO (1937, p. 60) presented a postscript about the environment where specimens were collected: “They were found from a well-like pit 13 m deep artificially (?) excavated on a reef [ … ] The bottom of the

deep pit, inhabited gregariously by this animal, is covered with mud which has the smell of hydrogen sulphide.” Both habitats around SMRC and MMBS, where our specimens were found, were a less-disturbed, sulfide-containing muddy sand bottom, roughly corresponding to that noted by SHIINO (1937). In add-ition, our observation of living A. nipponicus indicated that its habitat is restricted by the type of bottom substrate. Consider-ing SHIINO (1937) and our present results, A. nipponicus likely prefers (or may be confined to) a less-disturbed, sulfide-conta-ining muddy sand bottom. This probable specialized habitat may be one reason why so few records exist for this species.

ACKNOWLEDGMENTS

We thank Yasutaka TSUCHIYA, Toshihiko SATO, Hideo SHINAGAWA, Yutaro YAMADA, and Daisuke SHIBATA for help in collecting the tanaidaceans from experimental aquaria in SMRC; Morihiko TOMATSURI for help in sending live specimens collected in 2015; and Mamoru SEKIFUJI for help in sampling around MMBS in 2016.

REFERENCES

ALVARO, M. C., BŁAŻEWICZ-PASZKOWYCZ, M., DAVEY, N. & SCHIAPARELLI, S. 2011. Skin-digging tanaids: the unusual parasitic behavior of Exspina typica in Antarctic waters and worldwide deep basins. Antarctic Science, 23: 343–348.

BAMBER, R. N. 2012. A re-assessment of Hexapleomera DUDICH, 1931 (Crustacea: Tanaidacea: Tanaidae), with designation of three new species. Zootaxa, 3583: 51–70.

BŁAŻEWICZ-PASZKOWYCZ, M., BAMBER, R. N. & CUNHA, M. R. 2011. New tanaidomorph Tanaidacea (Crustacea: Peracarida) from submarine mud-volcanoes in the Gulf of Cadis (North-east Atlantic). Zootaxa, 2769: 1–53.

BŁAŻEWICZ-PASZKOWYCZ, M., KOBYŁECKA, E. & JENNINGS, R. N. 2015. Redescription of wood-associated tanaidacean Protanais birsteini (KUDINOVA-PASTERNAK, 1970) and its relationship within the Tanaididae. Deep-Sea Research II, 111: 333–342.

JAMBIO. 2016. http://www.shimoda.tsukuba.ac.jp/~jambio/

　　index.html [accessed 6 August 2016]KAJIHARA, H. & KAKUI, K. 2016. An overview of recent

marine-biodiversity research in Japan. In MOTOKAWA, M. & KAJIHARA, H. (eds.) Species Diversity of Animals in Japan, pp. 25–45. Springer, Berlin.

KAKUI, K. 2016. Review of the taxonomy, diversity, ecology, and other biological aspects of Order Tanaidacea from Japan and surrounding waters. In MOTOKAWA, M. & KAJIHARA, H. (eds.) Species Diversity of Animals in Japan, pp. 603–627. Springer, Berlin.

KAKUI, K. & HIRUTA, C. 2013. Selfing in a malacostracan crustacean: why a tanaidacean but not decapods. Naturwissenschaften, 100: 891–894.

LARSEN, K., GUŢU, M. & SIEG, J. 2015. Order Tanaidacea DANA, 1849. In VON VAUPEL KLEIN, J. C., CHARMANTIER-

　　DAURES, M. & SCHRAM, F. R. (eds.) Treatise on Zoology-　　Anatomy, Taxonomy, Biology. The Crustacea 5, pp.

249–329. Brill, Leiden.MCCLAIN, C. & BARRY, J. 2014. Beta-diversity on deep-sea

wood falls reflects gradients in energy availability. Biology Letters, 10: 20140129.

MORALES-VELA, B., SUÁREZ-MORALES, E., PADILLA-SALDÍVAR, J. & HEARD, R. W. 2008. The tanaid Hexapleomera robusta (Crustacea: Peracarida) from the Caribbean manatee, with comments on other crustacean epibionts. Journal of the Marine Biological Association of the United Kingdom, 88: 591–596.

NAKANO, H., KAKUI, K., KAJIHARA, H., SHIMOMURA, M., JIMI, N., TOMIOKA, S., TANAKA, H., YAMASAKI, H., TANAKA, M., IZUMI, T., OKANISHI, M., YAMADA, Y., SHINAGAWA, H., SATO, T., TSUCHIYA, Y., OMORI, A., SEKIFUJI, M. & KOHTSUKA, H. 2015. JAMBIO Coastal Organism Joint Surveys reveals undiscovered biodiversity around Sagami Bay. Regional Studies in Marine Science, 2 supplement: 77–81.

OKUTANI, T. 1994. Yama-Kei Field Books 8. Yama-Kei Publishers, Tokyo, 368 pp. [ In Japanese]

SHIINO, S. M. 1937. On Apseudes nipponicus n. sp. (Crustacea, Tanaidacea). Annotationes Zoologicae Japonenses, 16: 53–62.

は　じ　め　に

　サバ目サバ亜目サバ科サワラ族魚類は 3属 21種の現生種が知られており，海水生であるが，河口や 300 km上流のメコン川にも見られる（NELSON et al., 2016）．世界の熱帯から温帯の海域に生息し，サワラ属（Scomberomorus）魚類は東部大西洋に 1種，西部大西洋に 4種，東太平洋に 2種 ,インド－西太平洋に 11 種が分布する（COLLETTE and NAUEN, 1983; COLLETTE and RUSSO, 1985）．ニジョウサバ属（Grammatorcynus）魚類は 2 種が知られており，オーストラリアと北大西洋にそれぞれ分布する．カマスサワラ属（Acanthocybium）は 1 種で熱帯から温帯にかけて汎世界的に分布する（COLLETTE and NAUEN, 1983）．　本邦におけるサワラ族魚類化石は，ニジョウサバ属では尾部骨格が富山市の八尾層群黒瀬谷層（中新統）から報告されている（UYENO and FUJII, 1975）．サワラ属魚類では前上顎骨が岡山県津山市の勝田層群（中新統）から（大江ほか，1986），頭蓋骨，肩帯，肋骨，脊椎骨の一部が埼玉県秩父郡小鹿野町の秩父町層群（中新統）から産出しており（上野・

坂本，1985），石川県金沢市の大桑層（更新統）からも左上顎骨が報告されている（松浦，1996）．また，カマスサワラ属では頭蓋骨が岐阜県瑞浪市から，歯骨が土岐市の瑞浪層群（中新統）から産出している（大江ほか，1981）．国外では主にイギリスや中近東の古第三系などから産出しており（e.g. MONSCH, 2004; MONSCH and BANNIKOV, 2011），例えばサワラ属の化石種である Scomberomorus avitus BANNIKOV, 1985がトルクメニスタンの古第三系上部から，Scomberomo-rus avitus BANNIKOV, 1982 がカザフスタンの始新統から記載されている（BANNIKOV, 1982; 1985）．今回報告する標本は岡山県新見市西部から 1994 年に著者の一人である石垣によって発見されたもので，サバ科サワラ族に属するものと考えられる．なお，骨の部分の名称は須田（1991）に従った．

産地と層序

　岡山県新見市西方付近では基盤岩を不整合に覆って下部中新統の備北層群が分布しており，種々の斧足類，掘足類，腹足類，カメ類などの化石が豊富に産出している（e.g. 田

口ほか，1979；平山ほか，1982；1983；平山・田口，1994）．特に，2000 年ごろまでは新見市西部辻田の旧小野田セメント粘土採掘場跡は化石が豊富に産出することが知られていた．今回報告する化石はこの採泥跡地から発見されたもので，田口ほか（1979）の Loc. 4にあたる（Fig. 1）．田口ほか（2013）によれば化石産地の中新統を上田（1989）の備北層群是松層としていることから本標本は本層の暗灰色泥岩から産出したと考えられる．

記　　載

硬骨魚綱　Osteichthyes HUXLEY, 1880条鰭亜綱　Actinopterygii KLEIN, 1885真骨区　Teleostei MÜLLER 1845

サバ目　Scombriformes (Pelagia) MIYA et al., 2013サバ亜目　Scombroidei BLEEKER, 1859

サバ科　Scombridae RAFINESQUE – SCHMALTZ, 1815サワラ族　Scomberomorini STARKS, 1910カマスサワラ属　Acanthocybium GILL, 1862

Acanthocybium sp.

標本番号　KMNH (Kitakyushu Museum of Natural History and Human History)VP 100,335，左前上顎骨の一部

　本標本は上向突起（ascending process）が発達すること，骨の縁辺に歯が並ぶこと，上向突起の後ろに主上顎骨関節突起（articulation process for maxilla）があることから左前上顎骨と考えられる（Fig. 2）．前部が保存されており，後部は欠損する．上向突起の側面観は矢じり状で，その前縁はほぼ直線的である．上向突起の高さは 36.8 mm で後方へ

の傾きは約 43°である．骨の表面は全体的に磨耗しており，破損しているところもある．内側の関節面等は磨耗により残されていない．外側面は全体に緩やかに膨出するが，下半部は平面的である．　外側面の歯槽部分は骨で覆われているが，内側面の歯槽部分の骨は欠損し，象牙質が露出している．上向突起のすぐ後ろの部分に主上顎骨関節突起の膨らみが残されており，この部分が全体の中でもっとも厚く，厚さは 9.0 mmである．　関節突起より後ろの部分は上部が厚く，下方に向かって薄くなる．内側面は後方に向かうに従って下部が薄くなる．保存されている後部の一番低いところは 17.0 mmである．　歯は全体に磨耗しており，破損しているところもあるが，歯槽部分は象牙質で充填されている．歯のかなりの部分が磨耗しているため，それぞれの歯の境界が明確でないものもあるが，歯の水平断面は丸くなく，側偏し，歯は比較的大きい．また，前方のものほど小さい傾向にある．大きな歯のおおよその幅は 4.3 mmであり，小さな歯の幅はおよそ1.5 mmである．少なくとも 19本が確認できる．

考　　察

　本標本は歯があること，上向突起があることから真骨魚類の前上顎骨と考えられる．上向突起が矢じり状を呈することや残された後部に厚みがあること，関節突起より後方の部分は高さがほぼ一定であることなどからサバ科サワラ族に属するものと考えられる．　サワラ族はニジョウサバ属，サワラ属，カマスサワラ属からなり，サワラ属はカマスサワラ属と 17 の骨学的形質を共有することから姉妹群と考えられている（COLLETTE and RUSSO, 1985）．ニジョウサバ属の前上顎骨の歯の断面は扁

平せず丸いが（Fig. 3），サワラ属とカマスサワラ属では側偏する（Figs. 4, 5）．サワラ属では歯と歯の間は広く空いており，歯槽の中に次の小さな歯が見られる（Fig. 4）が，カマスサワラ属では歯と歯の間は空いていない（Fig. 5）．　本標本は歯が丸くなく，側扁すること，隙間なく並んでいる点ではサバ科サワラ族のカマスサワラ属に類似する（Figs. 2, 5）．本化石の個体は全長 166 cm のカマスサワラの前上顎骨との比較から推定全長はおよそ 140 cm と考えられる．　サワラ属魚類は岡山県津山市の勝田層群から前上顎骨が報告されており（大江ほか，1986），全体的な形状は今回の標本に類似する．しかし，勝田層群産の化石が 歯と歯の間が離れており，次の歯が形成される孔があるといったサワラ属の特徴を示すのに対し，新見産の本標本にはそのような特徴は見られない．また，埼玉県秩父郡小鹿野町の秩父町層群からサワラ属の頭蓋骨，肩帯，肋骨，脊椎骨の一部

が産出しているが，前上顎骨は産出していない（上野・坂本，1985）．　本邦における中新世のカマスサワラ属魚類化石は岐阜県の瑞浪層群から知られており，瑞浪市からは頭蓋骨が，土岐市からは歯骨が報告されているが，前上顎骨は産出していない（大江ほか，1981）．瑞浪層群のカマスサワラ属の歯骨の歯は大きさや並び方で本標本に類似しており，同一種の可能性も考えられる．　現生のカマスサワラ属魚類はカマスサワラ（Acanthocyb-ium solandri (CUVIER, 1829)） 1 種であるが，今回の化石はカマスサワラとは次の点で異なる．(1) 前上顎骨の歯はカマスサワラより大きい，カマスサワラの歯は比較的小さく，後方に向かうに従って次第に大きくなる．(2) 前上顎骨の口縁（下縁）前部は直線的であるが，カマスサワラでは緩やかに湾入する．

(3) 前上顎骨の上向突起前縁の後方への傾きが 43°とカマス 　 サワラに比べて大きく，Scomberomorus lineolatus（23° : DEVARAJ, 1975）を除くサワラ属の範囲内（32–61°: COLLET-TE and RUSSO, 1985）である．カマスサワラでは 34–37° （Co-LLETTE and RUSSO, 1985）であり，傾きがより小さい．　以上のように本種は歯が側扁し隙間なく並んでいることからカマスサワラ属の一員としたが，歯はカマスサワラよ

りも大きく，上向突起の形態ではむしろサワラ属に類似することから新たな属を考える必要があるかもしれない．本種はカマスサワラ属とサワラ属の系統関係やサワラ族魚類の起源と進化に関する知見を得る上で重要な種と考えられ，さらなる標本の産出が期待される．

謝　　辞

　本研究を進めるにあたり，国立科学博物館所蔵の現生骨格標本の観察にご協力いただいた国立科学博物館名誉研究員の上野輝彌博士ならびに標本資料センターディレクター及び分子生物多様性研究資料センター長の真鍋真博士に心より感謝の意を表する．また，水産大学校の須田有輔博士ならびに城西大学の宮田真也博士からは査読者として多くの貴重なコメントをいただいた．ここに記してお礼申し上げる．なお，本研究は JSPS 科研費 JP2640506（籔本）の助成を受けた．

文　　献

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Fig. 1. Apseudes nipponicus SHIINO, 1937. A, a live individual collected from an experimental aquarium for rearing a gastropod Strombus luhuanus at SMRC; B, a live animal under a natural environment (after the removal of a fist-sized rock) at a depth of 2 m around MMBS.

2 Keiichi KAKUI et al. Habitat of Apseudes nipponicus 3

INTRODUCTION

Apseudes nipponicus SHIINO, 1937 is the first described tanaidacean species in Japan (KAKUI, 2016). In Tanaidacea, most members of which are approximately a few millimeters in length (LARSEN et al., 2015), A. nipponicus is a relatively large-sized species, reaching 16 mm in length (SHIINO, 1937). This species has a digging-type pereopod 1 (cf. LARSEN et al., 2015), suggesting its burrowing mode of life. SHIINO (1937) described A. nipponicus based on specimens collected from a mud bottom at a depth of 13 m in Sagami Bay (off Hayama, Kanagawa), and also included data from several specimens from the Sagami Sea (Nabeta, Shizuoka).　　Sagami Bay and the Sagami Sea are the best studied marine areas in Japan (KAJIHARA & KAKUI, 2016). For about 40 years since the 1930s, HIROHITO, the Emperor Showa, had conducted faunal surveys of the area (A. nipponicus was described based on specimens collected during this survey). In recent years, JAMBIO, the Japanese Association for Marine Biology, has hosted a serial survey and actively investigated marine fauna around the Shimoda Marine Research Center (SMRC) of the University of Tsukuba, and the Misaki Marine Biological Station (MMBS) of the University of Tokyo, by

using grab-samplers, dredges, and sledge-nets (NAKANO et al., 2015). Thus far, nine surveys incorporating 59 sampling sites, ranging from 2 to 750 m in depth, have been conducted (NAKANO et al., 2015; JAMBIO, 2016).

Despite the large body size of this species and the great sampling efforts in Sagami Bay and the Sagami Sea, after SHIINO’ s (1937) original description, additional reports of A. nipponicus were very limited. The only published record is an illustrated encyclopedia (OKUTANI, 1994), which presented a photo of a live individual collected from a muddy bottom in shallow water around Hayama. A recent serial survey by JAMBIO around SMRC and MMBS col lected many tanaidaceans but failed to obtain any specimen of this species (K. KAKUI, unpublished data). In 2014, we discovered several individuals of A. nipponicus for the first time in decades, and also collected this species in 2015 and 2016. In this study, in addition to observations of living animals, we discuss the preferred habitat of this species.

MATERIALS AND METHODS

Sampling was performed at the SMRC on 16 May 2014 and 7 April 2015. The bottom substrates in experimental

aquaria for rearing a colonial ascidian Didemnum vexillum (in 2014) or a gastropod Strombus luhuanus (in 2015) were collected by a siphon and then filtered by a hand net, and tanaidaceans were picked up from the residue. Individuals found in 2014 were released into the sea after taking photos. Fifty specimens collected in 2015 were fixed by ethanol or formalin, about 140 tanaidaceans were sent live to KK’s lab at Hokkaido University and used to observe their burrowing behavior, while others were released into the sea. A scuba sampling around MMBS was carried out on 25 May 2016. The sampling site was at a depth of 2 m around a small pier for MMBS’s research boat (35° 9′ 27.507″ N, 139° 36′ 43.704″ E). Collected specimens were fixed in ethanol. Two fixed specimens collected from SMRC were deposited in the Kitakyushu Museum of Natural History & Human History (KMNH IvR 500921). In all samplings, the accompanying fauna was not checked.

Living individuals of A. nipponicus were kept at room temperature and under ambient light in the laboratory. As muddy sand substrates where our specimens were collected could not be prepared, and one congener (Apseudes sp.) has been successfully maintained in coral sand for years (KAKUI & HIRUTA, 2013), three size categories of coral sand (> 1 mm, 1–0.5 mm, and 0.5–0.3 mm in diameter; about 1,400 g/l) were used as bottom substrates. We also tested commercial aquarium gravel, Pure Black (JAN code 4972547010049, GEX, Japan; 2–4 mm in grain size, 750 g/l), as a bottom substrate. The behavior of animals was observed with the naked eye.

RESULTS AND DISCUSSION

In SMRC, A. nipponicus (Fig. 1A) was collected from a muddy sand bottom in experimental aquaria. This is the first record from an artificial environment for this species. A few specimens were found in 2014, and numerous (more than 190) individuals were collected in 2015. How they colonized the aquaria remains unclear. One possibility is that tanaidaceans were attached to the surface of colonial ascidians or gastropods when these were placed into the aquaria. Another possible route by which A. nipponicus may have entered the aquaria is via the intake hosepipe of sea-water which is placed near the sea-bottom at a sea depth of 3 m in front of the SMRC, at Nabeta Bay, where some of the type specimens were collected (SHIINO, 1937). As our sample included individuals of various sizes, some of which were ovigerous, A. nipponicus appears to reproduce in these aquaria. The bottom sand in the aquaria was black, indicating that it contains sulfide. Around MMBS, three specimens were collected. All specimens were found under fist-sized rocks partly buried in mud (Fig. 1B). This is the first in-situ observation of this species in a natural environment. The substrate under the rocks was blackish, sulfide-containing muddy sand.　　Rearing experiments showed that A. nipponicus could

burrow the artificial substrate covered by Pure Black (aquari-um gravel) but not coral sand, suggesting that there are usable and unusable bottom conditions for A. nipponicus. Incidenta-lly, a congener Apseudes sp. sensu KAKUI & HIRUTA (2013) was able to burrow into Pure Black as well as into coral sand (KAKUI & HIRUTA, 2013; K. KAKUI, unpublished data). This is the first evidence of differences in the burrowing ability among congeneric species.　　In Tanaidacea, the habitat preference of species is poorly understood. For species that were repeatedly collected from some specialized environments, their habitat preference has been suggested, such as the surface of sea turtles or manatees for some Hexapleomera species (MORALES-VELA et al., 2008; BAMBER, 2012), the inside of the body wall of deep-sea holothurians for Exspina typica LANG, 1968 (ALVARO et al., 2011), and deep-sea sunken woods for members of Protanais (MCCLAIN & BARRY, 2014; BŁAŻEWICZ-PASZKOWYCZ et al., 2015). BŁAŻEWICZ-PASZKOWYCZ et al. (2011) proposed that the genera Cristatotanais, Coalecerotanais, and Obesutanais supposedly are associated with and adopted to chemically-reduced habitats like mud-volcanoes, cold seeps, and hydrothermal vents. For A. nipponicus, SHIINO (1937, p. 60) presented a postscript about the environment where specimens were collected: “They were found from a well-like pit 13 m deep artificially (?) excavated on a reef [ … ] The bottom of the

deep pit, inhabited gregariously by this animal, is covered with mud which has the smell of hydrogen sulphide.” Both habitats around SMRC and MMBS, where our specimens were found, were a less-disturbed, sulfide-containing muddy sand bottom, roughly corresponding to that noted by SHIINO (1937). In add-ition, our observation of living A. nipponicus indicated that its habitat is restricted by the type of bottom substrate. Consider-ing SHIINO (1937) and our present results, A. nipponicus likely prefers (or may be confined to) a less-disturbed, sulfide-conta-ining muddy sand bottom. This probable specialized habitat may be one reason why so few records exist for this species.

ACKNOWLEDGMENTS

We thank Yasutaka TSUCHIYA, Toshihiko SATO, Hideo SHINAGAWA, Yutaro YAMADA, and Daisuke SHIBATA for help in collecting the tanaidaceans from experimental aquaria in SMRC; Morihiko TOMATSURI for help in sending live specimens collected in 2015; and Mamoru SEKIFUJI for help in sampling around MMBS in 2016.

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SHIINO, S. M. 1937. On Apseudes nipponicus n. sp. (Crustacea, Tanaidacea). Annotationes Zoologicae Japonenses, 16: 53–62.

は　じ　め　に

　サバ目サバ亜目サバ科サワラ族魚類は 3属 21種の現生種が知られており，海水生であるが，河口や 300 km上流のメコン川にも見られる（NELSON et al., 2016）．世界の熱帯から温帯の海域に生息し，サワラ属（Scomberomorus）魚類は東部大西洋に 1種，西部大西洋に 4種，東太平洋に 2種 ,インド－西太平洋に 11 種が分布する（COLLETTE and NAUEN, 1983; COLLETTE and RUSSO, 1985）．ニジョウサバ属（Grammatorcynus）魚類は 2 種が知られており，オーストラリアと北大西洋にそれぞれ分布する．カマスサワラ属（Acanthocybium）は 1 種で熱帯から温帯にかけて汎世界的に分布する（COLLETTE and NAUEN, 1983）．　本邦におけるサワラ族魚類化石は，ニジョウサバ属では尾部骨格が富山市の八尾層群黒瀬谷層（中新統）から報告されている（UYENO and FUJII, 1975）．サワラ属魚類では前上顎骨が岡山県津山市の勝田層群（中新統）から（大江ほか，1986），頭蓋骨，肩帯，肋骨，脊椎骨の一部が埼玉県秩父郡小鹿野町の秩父町層群（中新統）から産出しており（上野・

坂本，1985），石川県金沢市の大桑層（更新統）からも左上顎骨が報告されている（松浦，1996）．また，カマスサワラ属では頭蓋骨が岐阜県瑞浪市から，歯骨が土岐市の瑞浪層群（中新統）から産出している（大江ほか，1981）．国外では主にイギリスや中近東の古第三系などから産出しており（e.g. MONSCH, 2004; MONSCH and BANNIKOV, 2011），例えばサワラ属の化石種である Scomberomorus avitus BANNIKOV, 1985がトルクメニスタンの古第三系上部から，Scomberomo-rus avitus BANNIKOV, 1982 がカザフスタンの始新統から記載されている（BANNIKOV, 1982; 1985）．今回報告する標本は岡山県新見市西部から 1994 年に著者の一人である石垣によって発見されたもので，サバ科サワラ族に属するものと考えられる．なお，骨の部分の名称は須田（1991）に従った．

産地と層序

　岡山県新見市西方付近では基盤岩を不整合に覆って下部中新統の備北層群が分布しており，種々の斧足類，掘足類，腹足類，カメ類などの化石が豊富に産出している（e.g. 田

口ほか，1979；平山ほか，1982；1983；平山・田口，1994）．特に，2000 年ごろまでは新見市西部辻田の旧小野田セメント粘土採掘場跡は化石が豊富に産出することが知られていた．今回報告する化石はこの採泥跡地から発見されたもので，田口ほか（1979）の Loc. 4にあたる（Fig. 1）．田口ほか（2013）によれば化石産地の中新統を上田（1989）の備北層群是松層としていることから本標本は本層の暗灰色泥岩から産出したと考えられる．

記　　載

硬骨魚綱　Osteichthyes HUXLEY, 1880条鰭亜綱　Actinopterygii KLEIN, 1885真骨区　Teleostei MÜLLER 1845

サバ目　Scombriformes (Pelagia) MIYA et al., 2013サバ亜目　Scombroidei BLEEKER, 1859

サバ科　Scombridae RAFINESQUE – SCHMALTZ, 1815サワラ族　Scomberomorini STARKS, 1910カマスサワラ属　Acanthocybium GILL, 1862

Acanthocybium sp.

標本番号　KMNH (Kitakyushu Museum of Natural History and Human History)VP 100,335，左前上顎骨の一部

　本標本は上向突起（ascending process）が発達すること，骨の縁辺に歯が並ぶこと，上向突起の後ろに主上顎骨関節突起（articulation process for maxilla）があることから左前上顎骨と考えられる（Fig. 2）．前部が保存されており，後部は欠損する．上向突起の側面観は矢じり状で，その前縁はほぼ直線的である．上向突起の高さは 36.8 mm で後方へ

の傾きは約 43°である．骨の表面は全体的に磨耗しており，破損しているところもある．内側の関節面等は磨耗により残されていない．外側面は全体に緩やかに膨出するが，下半部は平面的である．　外側面の歯槽部分は骨で覆われているが，内側面の歯槽部分の骨は欠損し，象牙質が露出している．上向突起のすぐ後ろの部分に主上顎骨関節突起の膨らみが残されており，この部分が全体の中でもっとも厚く，厚さは 9.0 mmである．　関節突起より後ろの部分は上部が厚く，下方に向かって薄くなる．内側面は後方に向かうに従って下部が薄くなる．保存されている後部の一番低いところは 17.0 mmである．　歯は全体に磨耗しており，破損しているところもあるが，歯槽部分は象牙質で充填されている．歯のかなりの部分が磨耗しているため，それぞれの歯の境界が明確でないものもあるが，歯の水平断面は丸くなく，側偏し，歯は比較的大きい．また，前方のものほど小さい傾向にある．大きな歯のおおよその幅は 4.3 mmであり，小さな歯の幅はおよそ1.5 mmである．少なくとも 19本が確認できる．

考　　察

　本標本は歯があること，上向突起があることから真骨魚類の前上顎骨と考えられる．上向突起が矢じり状を呈することや残された後部に厚みがあること，関節突起より後方の部分は高さがほぼ一定であることなどからサバ科サワラ族に属するものと考えられる．　サワラ族はニジョウサバ属，サワラ属，カマスサワラ属からなり，サワラ属はカマスサワラ属と 17 の骨学的形質を共有することから姉妹群と考えられている（COLLETTE and RUSSO, 1985）．ニジョウサバ属の前上顎骨の歯の断面は扁

平せず丸いが（Fig. 3），サワラ属とカマスサワラ属では側偏する（Figs. 4, 5）．サワラ属では歯と歯の間は広く空いており，歯槽の中に次の小さな歯が見られる（Fig. 4）が，カマスサワラ属では歯と歯の間は空いていない（Fig. 5）．　本標本は歯が丸くなく，側扁すること，隙間なく並んでいる点ではサバ科サワラ族のカマスサワラ属に類似する（Figs. 2, 5）．本化石の個体は全長 166 cm のカマスサワラの前上顎骨との比較から推定全長はおよそ 140 cm と考えられる．　サワラ属魚類は岡山県津山市の勝田層群から前上顎骨が報告されており（大江ほか，1986），全体的な形状は今回の標本に類似する．しかし，勝田層群産の化石が 歯と歯の間が離れており，次の歯が形成される孔があるといったサワラ属の特徴を示すのに対し，新見産の本標本にはそのような特徴は見られない．また，埼玉県秩父郡小鹿野町の秩父町層群からサワラ属の頭蓋骨，肩帯，肋骨，脊椎骨の一部

が産出しているが，前上顎骨は産出していない（上野・坂本，1985）．　本邦における中新世のカマスサワラ属魚類化石は岐阜県の瑞浪層群から知られており，瑞浪市からは頭蓋骨が，土岐市からは歯骨が報告されているが，前上顎骨は産出していない（大江ほか，1981）．瑞浪層群のカマスサワラ属の歯骨の歯は大きさや並び方で本標本に類似しており，同一種の可能性も考えられる．　現生のカマスサワラ属魚類はカマスサワラ（Acanthocyb-ium solandri (CUVIER, 1829)） 1 種であるが，今回の化石はカマスサワラとは次の点で異なる．(1) 前上顎骨の歯はカマスサワラより大きい，カマスサワラの歯は比較的小さく，後方に向かうに従って次第に大きくなる．(2) 前上顎骨の口縁（下縁）前部は直線的であるが，カマスサワラでは緩やかに湾入する．

(3) 前上顎骨の上向突起前縁の後方への傾きが 43°とカマス 　 サワラに比べて大きく，Scomberomorus lineolatus（23° : DEVARAJ, 1975）を除くサワラ属の範囲内（32–61°: COLLET-TE and RUSSO, 1985）である．カマスサワラでは 34–37° （Co-LLETTE and RUSSO, 1985）であり，傾きがより小さい．　以上のように本種は歯が側扁し隙間なく並んでいることからカマスサワラ属の一員としたが，歯はカマスサワラよ

りも大きく，上向突起の形態ではむしろサワラ属に類似することから新たな属を考える必要があるかもしれない．本種はカマスサワラ属とサワラ属の系統関係やサワラ族魚類の起源と進化に関する知見を得る上で重要な種と考えられ，さらなる標本の産出が期待される．

謝　　辞

　本研究を進めるにあたり，国立科学博物館所蔵の現生骨格標本の観察にご協力いただいた国立科学博物館名誉研究員の上野輝彌博士ならびに標本資料センターディレクター及び分子生物多様性研究資料センター長の真鍋真博士に心より感謝の意を表する．また，水産大学校の須田有輔博士ならびに城西大学の宮田真也博士からは査読者として多くの貴重なコメントをいただいた．ここに記してお礼申し上げる．なお，本研究は JSPS 科研費 JP2640506（籔本）の助成を受けた．

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Fig. 1. Apseudes nipponicus SHIINO, 1937. A, a live individual collected from an experimental aquarium for rearing a gastropod Strombus luhuanus at SMRC; B, a live animal under a natural environment (after the removal of a fist-sized rock) at a depth of 2 m around MMBS.