Armostus ohyamatensis Hoshina and Satô, 2006

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

Armostus ohyamatensis Hoshina and Satô , new species

(Japanese name: Ôyamato-okatsuya-gamushi) ( Figs. 5, 13, 14, and 22)

Diagnosis. Body length is about 2 mm. Dorsum brown. Head and pronotum are minutely and densely punctate. Pronotum is very sparsely pubescent. Elytra are widest approximately 1/5 at base. All of 24 type specimens are females. A. ohyamatensis , new species, may have parthenogenetic reproduction.

Measurement of the Holotype. Body length 2.3 mm; head 0.52 mm in length (from base to front margin of clypeus) and 0.74 mm in width; pronotum 0.56 mm in length and 1.3 mm in width; elytra 1.5 mm in length and 1.4 mm in width.

Description. Coloration ( Fig. 13). General coloration of head and pronotum and elytra brown, in some specimens a little reddish; elytra with a sharply limited light brown spot on about basal 1/3 ( Fig. 13), showing small variations among specimens; clypeus lighter than vertex; maxillary palpi and labrum very light brown; antennae light brown with brown antennomere 1; legs brown with light brown tarsi; prosternum brown with a dark brown median carina; mesoventrite and abdominal ventrite brown; metaventrite dark reddish brown; legs brown with light brown tarsi. Body length 2.0– 2.3 mm, about 1.5 times as long as wide ( Fig. 5). Head about 1.4 times as wide as long, smooth, almost glabrous; vertex densely and minutely punctate ( Fig. 5); clypeus almost impunctate or punctate only in basal half; length and width of head about 0.91 times and 0.56 times as long as those of pronotum, respectively. Pronotum widest at base, about 2.2 times as wide as long ( Fig. 5), smooth, very finely, shortly, and sparsely pubescent ( Fig. 5); punctures of pronotum dense and minute, and their size almost of the same size ( Fig. 5); lateral margins simply curved and narrowing from base towards anterior margins; length and width of pronotum about 0.40 and 0.94 times as long as those of elytra, respectively. Scutellum smooth, impunctate or bearing a few very minute punctures. Elytra slightly longer than wide, widest approximately 1/5 at base ( Fig. 5), 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. Legs of normal shape as in other species of the genus Armostus . Prosternum less shining, impunctate, and strongly microreticulate, with a carina feebly curved at ventral margin in lateral view ( Fig. 17); mesoventrite less shining, impunctate, and strongly microreticulate except for preepisternal elevation of mesothorax; preepisternal elevation of mesothorax about 2.1 times as long as wide, shining, strongly punctate, very finely and shortly pubescent ( Fig. 22); metaventrite less shining, impunctate, and strongly microreticulate except for pentagonal middle portion; lateral sutures of metaventrite running very close to episternum and superficially not forming triangular area along each lateral margin as those of A. crenulatus ; pentagonal middle portion of metaventrite shining, punctate, and pubescent as preepisternal elevation of mesothorax ( Fig. 22); abdominal ventrite less shining, impunctate, strongly microreticulate; abdominal ventrite 1 with a distinct carina.

Distribution. Japan: Kyushu, Shikoku, and Honshu.

Type Series. Holotype, female, Mt. Fukuchi, Fukuoka Pref., Kyushu , 2. v. 1996, H. Hoshina leg. ( MNHA) . Paratypes, 1 female, same data as holotype except for collecting date, 30. VII. 1997 ; 1 female, same data as holotype except for collecting date, 27. X. 1997 ; 7 females, Mt. Yukawayama, Fukuoka Pref., Kyushu , 30. V. 1997, H. Hoshina leg. ; 2 females, Fujio-Jinja, Takamatsu City, Kagawa Pref., Shikoku , 2. VI. 2001, M. Maruyama leg. ; 6 females, Taniguchi, Ôtsu City , Shiga Pref., Honshu, H. Hoshina leg. (3 paratypes are preserved in LBM) ; 1 female, Yokohama National University, Yokohama City, Kanagawa Pref., Honshu , 18. VII. 2000, H. Hoshina leg. ; 1 female, Ôiso, Kanagawa Pref., Honshu , 23. XI. 1984, Y. Hirano leg. (YH) ; 2 females, Hayama, Kanagawa Pref., Honshu , 18. IX. 1989, H. Hamada leg. (YH) ; 2 females, Kôkyo- Fukiage-Gosho, Tokyo Pref., Honshu , 17. V. 2000, Y. Watanabe leg. (YH) . Type series of which deposit institutions are not specified are preserved in FU.

Remarks. Armostus ohyamatensis , new species, is very similar to A. crenulatus , but can be separated from the latter by having the large body (2.0– 2.3 mm), elytra slightly longer than wide ( Fig. 5), and preepisternal elevation of mesothorax about 2.1 times as long as wide ( Fig. 22). In contrast, A. crenulatus has a small body (1.7–2.0 mm), elytra almost as long as wide ( Fig. 4), and preepisternal elevation of mesothorax about 3.0 times as long as wide ( Fig. 20). Most of Japanese specimens of A. crenulatus is less than 2 mm in body length irrespective of sexes, therefore those two species can be distinguished based on the body size. Moreover, A. ohyamatensis new species resembles A. arcuatus Hebauer, 2001 in appearance, but can be distinguished from the latter by having the long-oval preepisternal elevation of mesothorax ( Fig. 22), whereas in A. arcuatus , it is very slender. Type series collected by the senior author were caught by sifting litter layers in the forests.

Etymology. The specific name is derived from an old expression indicating ‘‘Japan’’, Ôyamato.