Hydrovatus onigiri Watanabe and Biström, 2022

Watanabe, Kohei & Biström, Olof, 2022, A New Species of the Genus Hydrovatus Motschulsky (Coleoptera: Dytiscidae) from Japan, The Coleopterists Bulletin 76 (1), pp. 115-121 : 116-120

Hydrovatus onigiri Watanabe and Biström , new species zoobank.org/ urn:lsid:zoobank.org:act:2F488CF6-1DD9-4248-A5AC-371249C618B1 [Japanese name: Onigiri-maru-keshi-gengorô] ( Figs. 1A–B , 2A , 3A , 4A–D )

Hydrovatus subtilis Sharp, 1882 : Kawano et al. 2006: 31 [in part; misidentification]; Hayashi 2007: 80 [in part; misidentification]; Hayashi 2008: 62 [in part; misidentification]; Hayashi 2009: 237 [in part; misidentification]; Watanabe 2016: 53–55 [misidentification]; Watanabe and Hisamatsu 2016: 3 [misidentification]; Aimoto 2018: 186 [misidentification].

Type Material. Holotype: 1♂ ( NMNS), Shikatamen, Saza-cho, Kitamatsuura-gun, Nagasaki Pref., 25.V.2014, G. Fukagawa leg. Paratypes: [ Honshu ] Niigata Pref .: 2 exs. ( KWC), Ojiya-shi , 22.IX.2017, S. Watanuki leg. Ishikawa Pref. : 6 exs. ( IIM), Kodomari , Misaki-machi, Suzu-city, 14.VI.2016, K.Watanabe leg. ; 7 exs. ( KWC, FMNH), ditto, 28.VIII.2016, K. Watanabe leg. , Hydrovatus subtilis (text in Japanese); 7 exs. ( EUMJ, KWC), Awazu , Misaki-machi, Suzu-shi, 27.VI.2017, K. Watanabe leg. Aichi Pref. : 1 ex. ( SSC), Higashihosoya-cho , Toyohashi-shi, 23.IX.2017, S. Sano leg. Mie Pref. : 1 ex. ( EUMJ), Hazama , 3.X.1965, M. Satô leg. , Hydrovatus subtilis Sharp Det. M Satô 1984 ; 9 exs. ( KAC), Funakoshi-ike , Daiô-cho, Shimashi, 14.V.2005, K. Akita leg. ; 32 exs. ( KAC), ditto, 3.IX.2005, K.Akita leg. ; 4 exs. ( KAC), ditto, 3.V.2007, K. Akita leg. ; 6 exs. ( KAC), ditto, 26.VIII.2013, K. Akita leg. ; 5 exs. ( KWC), ditto, 15.VIII.2016, Kohei Watanabe leg. , Hydrovatus subtilis (text in Japanese); 2 exs. ( KAC), Hokke , Ueno-C., 4.VI.1993, K.Akita leg. ; 10 exs. ( KAC), 240 m, Yûmen , Ayamacho, Iga-shi, 8.X.2011, K. Akita leg. ; 1 ex. ( JNC), Ikeyama , Kameyama-shi, 19.VIII.2002, J. Nakajima leg. ; 2 exs. ( IIM), Makiyama , Iga-shi, 20.VI.2021, K. Kawamura leg. 3 exs. ( KWC), 190 m, Oki , Iga-shi, 22.X.2019, Shotaro Tsuda leg. ; 1 ex. ( KWC), 250 m, Takayama , Iga-shi, 25.VIII.2019, Shotaro Tsuda leg. Wakayama Pref. : 2 exs. ( WMNH, INS-27745), Tahara , Koza-cho, 23.VII.1993, I. Matoba leg. ; 1 ex. ( WMNH, INS-27746), Pond , Kurosawa-yama, 26.IV.1997, Isao Matoba leg. ; 2 exs. ( WMNH, INS-1258), Nunoike , Kanaya-cho, 20.X.1993, I. Matoba leg. Osaka Pref. : 1 ex. ( KWC), Pond A, Minami-ku , Sakai-shi, 19.IV.2017, M. Suzuki leg. ; 2 exs. ( KWC), ditto, 12.VII.2017, M. Suzuki leg. ; 1 ex. ( KWC), Pond B, Minami-ku , Sakai-shi, 19.IV.2017, M. Suzuki leg. ; 1 ex. ( KWC), ditto, 12.VII.2017, M. Suzuki leg. ; 4 exs. ( KWC), Pond C, Ibaraki-shi , 21.V.2017, M. Suzuki leg. ; 5 exs. ( KWC), Panasonic-biotope , Kadoma-shi, 25.IV.2017, M. Suzuki leg. ; 1 ex. ( KWC), ditto, 19.VII.2013, M. Suzuki leg. ; 1 ex. ( KWC), ditto, 12.XI.2012, M. Suzuki leg. Hyogo Pref. : 4 exs. ( KAC), Aonogahara , Ono-shi, 25.VIII.1991, A. Kitayama leg. ; 2 exs. ( KAC), Aonogahara , Kasai-shi, 16.V.1992, A. Kitayama leg. Okayama Pref. : 1 ex. ( KWC), Tanematsuyama , Tsubue, Kurashiki-shi, 27.VIII.2017, H. Suenaga leg. ; 2 exs. ( KWC), ditto, 30.X.2017, K. Watanabe leg. Hiroshima Pref. : 1 ex. ( HMNS), Misonou , Saijo-cho, Higashihiroshima-shi, 7.XI.2009, Y. Akiyama leg. ; 1 ex. ( HMNS), Kagamiyama , Saijo-cho, Higashihiroshima-shi, 7.XI.2014, Y. Akiyama leg. ; 4 exs. ( KWC), ditto, 1.XI.2008, S. Shimazoe leg. ; 2 exs. ( HMNS), Okuda , Saijo-cho, Higashihiroshima-shi, 12.X.2009, Y.Akiyama leg. ; 2 exs. ( HMNS), Kanmuri , Siwa-cho, Higashihiroshima-shi, 19.VII.2000, M. Sakamoto leg. ; 2 exs. ( JNC), Hachihonmatsu-cho , Higashihiroshima-shi, 1.VI.2017, N. Shimura leg. ; 1 ex. ( HMNS), Sera-cho , 26.VIII.2001, Y.Akiyama leg. ; 3 exs. ( HMNS), ditto, 23.IX.2001, Y. Akiyama leg. Shimane Pref. : 2 exs. ( HOWP), Biotope , Okinoshima , Sono-cho, Izumo-shi, 19.VI.2008, M. Hayashi leg. ; 2 exs. ( HOWP), ditto, 18.V.2008, M. Hayashi leg. ; 1 ex. ( HOWP), ditto, 23.VIII.2008, M. Hayashi leg. ; 2 exs. ( HOWP), ditto, 13.V.2008, M. Hayashi leg. ; 1 ex. ( HOWP), ditto, 18.VII.2008, M. Hayashi leg. ; 2 exs. ( HOWP), ditto, 4.VI.2008, M. Hayashi leg. ; 3 exs. ( HOWP), Hata , Nozato-cho, 4.X.2003 ; 2 exs. ( HOWP), ditto, 20.IV.2007, M. Hayashi leg. ; 2 exs. ( HOWP), Ichibatayakushi , Kozakai-chi, Izumo-shi, 17.V.2008, M. Hayashi leg. ; 2 exs. ( HOWP), Kiamicho , Masuda-shi, 29.IX.2009, Kawano, Ooki and Aoki leg. ; 4 exs. ( HOWP), Wadakami , Okuuga-cho, Izumo-shi, 9.IX.2006, M. Hayashi leg. Yamaguchi Pref. : 24 exs. ( KWC), Sasanami , Hagi-shi, 9.VII.2017, A. Aimoto leg. ; 4 exs. ( KWC), Tachikuma , Yoshimi, Ube-shi, 29.VII.2017, A. Aimoto leg. ; 8 exs. ( KWC), Yashiro , Shunan-shi, 5.VIII.2017, A. Aimoto leg. ; 2 exs. ( KWC), Yamanaka , Ube-shi, 24.VII.2014, D. Inoue leg. ; 6 exs. ( HOWP), Yaji , Toyota-cho, Shimonoseki-shi, 16.VIII.2008, M. Hayashi leg. [ Shikoku ] Kagawa Pref .: 6 exs. ( HFC, KWC), Danyama , Kounoura , Shodoshima-cho, Shodoshima- Island, 18.VIII.2018, H. Fujimoto leg. Ehime Pref. : 1 ex. ( KWC), Miaki , Iyo-City, 24.VIII.2008, K. Watanabe leg. , Hydrovatus subtilis (text in Japanese); 1 ex. ( KWC), Nagasawa , Imabari-shi, 27.VIII.2012, Y. Koshiyama leg. Kochi Pref. : 14 exs. ( KWC, MMC), Usa , Tosa-shi, 30.IX.2016, M. Mori leg. ; 2 exs. ( MMC), Unoe , Nakamura-shi, 4.V.1992, M. Mori leg. [ Kyushu ] Fukuoka Pref .: 1 ex. ( EUMJ), Fukuoka , 4.V.1958 .; 1 ex. ( MMC), Shimotobaru , Koge-machi, 1.X.2010, M. Mori leg. ; 1 ex. ( KMNH), Yoshii , Ukiha-gun, Chikugo, 8.VII.1961, N. Gyotoku leg. ; 1 ex. ( KMNH), Yoshii , Chikugo, 10.VII.1953, N. Gyotoku leg. Nagasaki Pref. : 3 exs. ( KWC), Yukinourakoubutsugou , Ooseto-cho, Saikai-shi, 11.V.2014, G. Fukagawa leg. ; 2 exs. ( KWC), Fuufuike , Ooseto-cho, Saikai-shi, 27.IV.2014, G. Fukagawa leg. ; 1 ex. ( KWC), same locality as for the holotype, 25.V.2014, G.Fukagawa leg. , Hydrovatus subtilis Det. Kohei Watanabe 2017 (text in Japanese); 3 exs. ( KWC), Aigawa-machi , Nagasaki-shi, 20.IV.2014, G. Fukagawa leg. , Hydrovatus subtilis Det. Kohei Watanabe 2017 (text in Japanese); 3 exs. ( KWC), Miiraku-machi , Goto-shi, Fukue-jima Island, 18.VI.2016, S. Ohba leg. ; 3 exs. ( KWC), Hamanokuri , Miiraku-machi , Goto-shi, Fukue-jima Island, 18.VI.2016, S. Ohba leg. ; 9 exs. ( KWC), Hamanokuri , Miiraku-machi , Goto-shi, Fukue-jima Island, 4.VIII.2017, S. Ohba leg. ; 1 ex. ( KWC), Oohama , Uku-jima Island, 6.VIII.2011, Gentarou Fukagawa leg. ; 1 ex. ( KAC), Uragashira , Fukue-jima Island, Goto, 24.VIII.2001, M. Nishida leg. Miyazaki Pref. : 15 exs. ( NMNS), Nakakanbaru , Sadowara-cho, 21.V.1994, Kinoda and Nomura leg. ; 1 ex. ( NMNS), Nakakanbara , Sadowara, 21.V.1994, S. Nomura leg. ; 2 exs. ( EUMJ), Kiyotake , 6.VIII.1954, Y. Maeda leg. [ Tsushima Is. ] 1 ex. ( JNC), Tanohama , Kamiagatacho, Tsushima-shi, 28.VIII.2017, J. Nakajima leg.

Description, Male. Body habitus (dorsal aspect) ( Fig. 1B ): Shape compact and somewhat globular. Laterally, body evenly curved (angle between pronotum and elytron indistinct). Entire upper surface slightly dull (not shiny). Total length 2.52–2.72 mm, width 1.58–1.68 mm. Coloration: Head and pronotum somewhat paler than elytra, pale ferrugineous to ferrugineous; pronotum basally in middle with vague, narrow dark ferruginous area. Elytra dark ferruginous, laterally slightly paler but without distinct color pattern ( Figs. 1B , 2A ). Epipleura ferruginous. Venter pale ferruginous to ferruginous. Head: Outline between eyes almost evenly curved; medially slightly less so. Not margined but medially close to frontal edge with some transverse punctures forming a vague, medially broken impression. Surface of head with two vague depressions frontally at eyes; covered with microsculpture, the meshes of which are roughly isodiametric and their size somewhat variable (largest in area posteriorly at eyes and finest, in medial area posterior to frontal edge); with fine, sparse and scattered punctures (densest in shallow depressions of head and nar- rowly along eyes). Male antenna slightly modified with enlarged antennomeres. Antennomeres 4–6 broadest; from there towards apex antennomeres become gradually slightly narrower ( Fig. 4A ). Pronotum: Lateral outline slightly and evenly curved; finely margined. Surface covered with microsculpture, meshes of which are roughly isodiametric and of almost equal size; with quite fine punctures (slightly coarser and denser than on head), discally slightly sparser than close to prono- tal margins. Elytra: Surface covered with microsculpture, meshes roughly isodiametric and of almost equal size; with quite distinct and dense, almost evenly distributed punctures (slightly coarser than on pronotum) ( Fig. 2A ). Punctures become slightly finer posteriorly and laterally. No rows of punctures formed on disc. Epipleura finely microsculptured and with rather indistinct punctures. Ventral aspect: Prosternal process forming an equilateral triangle, frontally flat and at middle of posterior margin slightly enlarged. Metathorax and metacoxal plates with quite rough and dense punctures. Surface with distinct microsculpture (meshes clearly discernible; their shape laterally slightly elongated).Abdomen, except basally, with scattered, fine punctures. Narrow and fine stridulatory apparatus located in region where metathorax and metacoxal plates meet. Each file consists of about 15 very fine, narrow ridges which are not elevated from level of body surface. Legs: Pale ferrugineous to ferrugineous. Pro- and mesotarsi slightly enlarged, claws somewhat curved and slightly extended. Male genitalia: Penis (dorsal aspect) laterally slightly and evenly curved towards apical part which is almost parallel (about 1/4 of penis total length). Extreme apex with sides strong- ly curved inwards (apex appears blunt) ( Fig. 4B ). Penis in lateral aspect in apical 1/4 slightly curved upwards to apex which is hooked (hook bent almost 90 degrees) ( Fig. 4C ). Paramere apically with a distinct, well sclerotized hook; in figure most of it is covered by a thin and soft tissue ( Fig. 4D ).

Female. Antenna slender; lacks enlarged antennomeres. Stridulatory apparatus lacking. Pro- and mesotarsus slightly narrower than in male.

Distribution. Japan: Honshu, Shikoku, Kyushu, Tsushima Island ( Fig. 5 ).

Etymology. The species name is derived from the typical Japanese food “onigiri ”, in reference to the shape of prosternal process.

Diagnosis. The male antenna differs in shape between H. subtilis and H. onigiri as follows. In both species, the male antenna is medially enlarged, but in H. onigiri the fourth to sixth antennomeres are the broadest ( Fig. 4A ), while in H. subtilis , the sixth to eighth antennomeres are the broadest ( Fig. 4E ). The elytral punctures of H. subtilis ( Fig. 2B ) are slightly finer, less impressed, and denser than those of H. onigiri ( Fig. 2A ). Moreover, the body shape is slightly different, with the outline in the dorsal aspect being more streamlined in H. onigiri ( Figs. 1A–B ) than in H. subtilis ( Fig. 1C ) (the angle between the pronotum and elytra is small but often still discernible). The stridulatory apparatus of H. onigiri is poorly developed compared to the cor- responding structure of H. subtilis ; in H. subtilis , ridges number 12–14, especially the ridges in middle, are distinct, much more robust, and clearly elevated from the level of the body surface. The median lobes of the penis are quite similar, except for the extreme apex of the penis (frontal aspect); in H. subtilis , it has an angled outline ( Fig. 3B ), while it is almost evenly curved in H. onigiri ( Fig. 3A ).

Notes. In some males, the stridulatory apparatus is absent. Several specimens were collected by light trapping.

Remarks. Hydrovatus adachii Kamiya, 1932 was introduced as a separate species by Kamiya (1932), who described it on the basis of a single specimen with the following collecting data: “Honshu, Tokyo, [Musashi] 1♂, 20th. viii, 1929 (T. Adachi)”. Hydrovatus adachii was compared, although no type was available, with the type specimen of H. subtilis , and it was found to be conspecific with it ( Satô 1984). The holotype (kept in Tokyo University of Agriculture) of H. adachii was lost during or after the Second World War ( Mita et al. 2015; Nilsson and Hájek 2021). Therefore, it is impossible to solve the identity of H. adachii .

Figures

Fig. 1. Dorsal view of Hydrovatus species. A–B) H. onigiri, new species, C) H. subtilis. A) Paratype, female, B) Holotype, male, C) Lectotype, male. Photo credit: P. Malinen.

Fig. 2. Elytral punctures and microsculpture of Hydrovatus species.A) H. onigiri, new species, B) H. subtilis. Photo credit: P. Malinen.

Fig. 3. Apical view of penis apex. A) Hydrovatus onigiri, new species, B) H. subtilis. Photo credit: P. Malinen.

Fig. 4. Male genitalia and antennae of Hydrovatus species.A–D) H. onigiri, new species, E) H. subtilis. A, E) Male antenna, B) Penis, dorsal view, C) Penis, lateral view, D) Paramere. Scale bars = 0.5 mm, top scale is for male genitalia and bottom scale is for antennae.

Fig. 5. Distribution map of Hydrovatus species. Circle, H. onigiri, new species; triangle, H. adachii (= H. subtilis).