Hydraena (Hydraenopsis) formula Orchymont 1932
Creators: name: Jäch, Manfred A.
name: Díaz, Juan A.
name: Skale, Andre
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydraenidae
Hydraena
Hydraena formula

description: Hydraena (Hydraenopsis) formula Orchymont, 1932   
(Figs. 9, 14, 15, 17)  
 Hydraena formula Orchymont, 1932: 655; Hansen, 1998; Jäch et al., 2000.   
 Type locality. — Lac Thô, Hòa Bình Province, northern Vietnam.   
  Type material. —  Holotype male (ISNB, examined): “ ”, “Lac Tho [handwritten] Tonkin De Cooman [printed]”, “ A. d’Orchymont det [printed] H. formula TYPE [handwritten]”, “TYPE” [red], “Prép. micr. N° 710709.13” [green], “AEDEAGUS DRAWN BY P.D.PERKINS” [printed]. Paratypes (ISNB, examined): 1 male (aedeagus lacking), 2 females, same locality data as holotype.   
 Additional material examined. — SINGAPORE: 1 female (ZRC): Bukit Timah Nature Reserve, coll. Lua, 2 Apr.1997 “NS 224”; 1 female (ZRC): same locality, but coll. Lua et al., 13 Dec.1995 “NS 214”; 1 female (ZRC): Rifle Range Road, east of Bukit Timah, coll. C. M. Yang et al., 27 May 1993 “417 ZRC.6.18870 (NS102)”; 1 female (ZRC): Nee Soon Swamp Forest, coll. D. H. Murphy & C. M. Yang, 16 Apr.1992 “Y790”; 1 male, 1 female (NMW, ZRC): same locality, but coll. K. L. Yeo, 6 May 1992 “424 Y794D”.   
 Diagnosis. — Habitus and colouration as in H. undulata Jäch & Díaz, 1998 (see Jäch & Díaz, 1998: Fig. 7), 1.40– 1.50 mm long. See original description of the latter for details of external characters (Jäch & Díaz, 1998: 167).   
Male terminal sternite and spiculum (Fig. 9e): Sternite firmly connected with spiculum, resembling a contrabass; apex slightly emarginate.  
 Aedeagus (Fig. 9a–c): Very similar to that of H. undulata from Taiwan (see Jäch & Díaz, 1998: Fig. 20a–d). It differs from the latter mainly in the following characteristics: Distal lobe with spiny apex. Both parameres shorter, right one more setose than in H. undulata.   
 Gonocoxite (Fig. 9f) and female tergite X (Fig. 9g) more or less as in H. undulata (see Jäch & Díaz, 1998: Fig. 20e). Cavea of inner plate of gonocoxite undivided in the specimens examined.   
 Spermatheca (Fig. 9h–i) not distinguishable from that of H. undulata.   
Secondary sexual characters: Male forecoxa with a very small projection directed ventrad. Male mesoventrite slightly more deeply impressed between mesoventral disc and mesoventral process. Male mesoventral process more slender. Male metaventral plaques (Fig. 14) very thin, carinate. Male tergite X widely and asymmetrically excavate apically (excavation distinctly deeper on left side); dorsal apical margin asymmetrically and sinuously emarginate (more strongly emarginate on left side); corners subacute, right corner hardly noticeably longer than left one.  
Variability: In the specimens from Sumatra, the apical segment of the maxillary palpi is brownish subapically. In most of the few specimens examined from Singapore the apical segment of the maxillary palpi is more or less unicoloured yellowish, which may be due to tenerality.  
In some of the males, the hind tibia is hardly noticeably curved subapically and widened apically.  
 Distribution. — This species is obviously wide-spread in the Oriental Region, from Nepal to South China and western Indonesia.   
 In Singapore (Fig. 15), H. formula was collected in the Bukit Timah Reserve, near the Rifle Range Road (east of Bukit Timah), and in the Nee Soon Swamp Forest.
description: Published as part of Jäch, Manfred A., Díaz, Juan A. & Skale, Andre, 2013, The Hydraenidae (Coleoptera) Of The Republic Of Singapore, pp. 53-71 in Raffles Bulletin of Zoology 61 (1) on pages 54-55, DOI: 10.5281/zenodo.5351598