Armostus crenulatus (Régimbart 1903)

Hoshina, Hideto & Satô, Masataka, 2006, A Taxonomic Study of the Genus Armostus (Coleoptera: Hydrophilidae) from Japan, The Coleopterists Bulletin 60 (2), pp. 95-104 : 100-102

Armostus crenulatus (Régimbart 1903)

(Japanese name: Ajia-okatsuya-gamushi) ( Figs. 4, 9–12, 16, 20, 21, 25, 30, and 31)

Cercyon crenulatus Régimbart 1903:337 .

Armostus crenulatus: d’Orchymont 1926:208 ; d’Orchymont 1942:8; Hansen 1999 a:271; Hebauer 2001:38.

Diagnosis. Body length is less than 2 mm. Dorsum is brown. Head and pronotum are strongly and densely punctate. Pronotum is very sparsely pubescent. Elytra are widest approximately 1/3 at base.

Redescription. Coloration ( Figs. 9–12). Head and pronotum brown; elytra brown approximately 2/3 on base and light brown on apical approximately 1/3, often with a blackish patch on the central area, showing a certain variations among specimens ( Figs. 9 and 10), and most frequent coloration of elytra shown on Figs. 9 or 11, rarely concolorous brown as shown in Fig. 12; maxillary palpi very light brown; antennae light brown; legs brown with light brown tarsi. Body 1.7–2.0 mm in length, usually less than 2 mm, about 1.5 times as long as wide ( Fig. 4); head smooth, almost glabrous, and minutely and densely punctuate, but almost impunctate or sparsely punctate on apical half of clypeus; pronotum smooth and punctate, very sparsely, finely, and shortly pubescent ( Fig. 4); all the punctures of pronotum almost of the same size; scutellum smooth, and impunctate or having a few very minute punctures; elytra almost as long as wide, widest about 1/3 at base, simply curved at lateral margins, smooth, and very finely and 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 high and its ventral margins feebly curved in lateral view ( Fig. 16); preepisternal elevation of mesothorax about 3.0 times as long as wide, shining, strongly punctate, very finely and very shortly pubescent ( Fig. 20); lateral sutures of metaventrite running very close to episternum, but easily visible when removing episternum ( Fig. 21), therefore superficially not forming triangular area along each lateral margin ( Fig. 20); pentagonal middle portion of metaventrite shining, punctuate, and pubescent as preepisternal elevation of mesothorax ( Fig. 20); abdominal ventrite 1 with a distinct carina; male genitalia as shown in Figs. 25, 30, and 31.

Distribution. Japan: Ryukyus (Ishigaki Is. and Iriomote Is.) and Kyushu (?), India, Indonesia, Malaysia, Singapore, Nepal.

Specimens Examined. Paratype, 1 female, Mahe´, Juillet , 1901, collected from Indonesia (preserved in the collection of Institut royal des Sciences naturelles de Belgique, Bruxelles) ; 23 specimens, Mt. Omotodake , Ishigaki Is., 3. III. 2003, H. Hoshina leg. ; 24 specimens, Mt. Fukai-Omotodake , Ishigaki Is., 4. III. 2003, H. Hoshina leg. ; 8 specimens, Kanoirah , Iriomote Is., 16. X. 1988, S. Nomura leg. All specimens except for one paratype are preserved in FU .

Remarks. Armostus crenulatus (Régimbart, 1903) is recorded for the first time from the Ryukyus. d’Orchymont (1942) first reported this species from Japan based on specimens collected in Kyushu. However, no specimen of this species has been found in Kyushu since then. Though we have not examined Japanese specimens identified by d’Orchymont, we suppose that the Japanese specimens mentioned by d’Orchymont (1942) from Japan do not belong to A. crenulatus , but to a closely related species, A. ohyamatensis , new species. Forty-seven specimens from Ishigaki Is. were collected by sifting litter layers in the forests.