Armostus schenklingi (d’ Orchymont, 1914)

Hoshina, Hideto & Satô, Masataka, 2006, A Taxonomic Study of the Genus Armostus (Coleoptera: Hydrophilidae) from Japan, The Coleopterists Bulletin 60 (2), pp. 95-104 : 96-97

Armostus schenklingi (d’ Orchymont, 1914)

(Japanese name: Tsumaki-okatsuya-gamushi) ( Figs. 2, 6, 7, 14, 18, 23, 26, and 27)

Cercyon (Cercyon) Schenklingi d’Orchymont 1914:323 .

Armostus schenklingi: d’Orchymont, 1926:208 ; d’Orchymont 1942:10; Hansen 1999 a:271.

Diagnosis. Body length is about 2.5 mm. Dorsum is black or dark brown except for apical brownish spot. Head and pronotum are strongly and densely punctate. Pronotum is very sparsely pubescent. Elytra are widest approximately 1/3 at base.

Redescription. Coloration ( Figs. 6 and 7). Dorsum bicolorous; head and pronotum usually black or dark brown, rarely brown; pronotum sometimes lighter than head and elytra; main area of elytra usually black or dark brown, rarely brown, with reddish brown or brown small patches near humeri; apical area of elytra bearing a bright yellowish brown spot showing a certain variability in its extent ( Figs. 6 and 7); maxillary palpi very light brown; antennae light brown and terminal three or four segments darker than others; legs reddish brown or dark brown with light brown tarsi. Body 2.2–2.6 mm in length, about 1.6 times as long as wide ( Fig. 2); head smooth, minutely and densely punctate and very sparsely, finely, and shortly pubescent ( Fig. 2); pronotum smooth, punctuate, and pubescent as on head; all the punctures of pronotum almost of the same size; scutellum smooth, and impunctate or bearing a few very minute punctures; elytra a little longer than wide, widest approximately 1/3 at base, simply curved at lateral margins, smooth and very finely and very shortly pubescent, almost impunctate between striae; basal starting point of striae 6, 8, and 9 separated from base of elytra more distant than other striae; striae 9 and 10 invisible in dorsal view; hind wings fully developed; carina of prosternum low and its ventral margins almost straight in lateral view ( Fig. 14); preepisternal elevation of mesothorax about 2.4 times as long as wide, shining, strongly punctate, very finely and shortly pubescent ( Fig. 18); metaventrite with lateral sutures running distant from episternum, and forming triangular area along each lateral margin ( Fig. 18); pentagonal middle portion of metaventrite shining, punctuate, and pubescent as preepisternal elevation of mesothorax ( Fig. 18); abdominal ventrite 1 with a distinct carina; male genitalia as shown in Figs. 23, 26, and 27.

Distribution. Japan: Ryukyus (Okinawa Is., Ishigaki Is., Iriomote Is., and Yonaguni Is.), Taiwan, and Indonesia (Borneo, Java, Sumatra, Sumbawa, Sulawesi).

Specimens Examined. Paratypes, 6 specimens, Taihorin, Juli, 1911 collected from Taiwan (preserved in the collection of the Institut Royal des Sciences naturelles de Belgique, Bruxelles) . 8 specimens, Yona , Okinawa Is., 7–9. V. 1975, Y. Notsu leg. ; 28 specimens, Nakasuji , Ishigaki Is., 13. III. 2000, T. Kurihara leg. ; 1 specimen, Mt. Bannadake , Ishigaki Is., 14–15. V. 1975, Y. Notsu leg. ; 60 specimens, from Ôhara to Otomi , Iriomote Is., 30–31. V. 1974, M. Satô leg. ; 1 specimen, Yonaguni Is. , 12. VI. 1965, K. Iha leg. All specimens except for paratypes are preserved in FU.

Remarks. This species is recorded for the first time from Japan.