Hydraena (Hydraenopsis) jacobsoni 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 jacobsoni

description: Hydraena (Hydraenopsis) jacobsoni Orchymont, 1932   
(Figs. 10, 15–17)  
 Hydraena jacobsoni Orchymont 1932: 656; Fernando & Gatha, 1963; Hansen, 1998; Jäch et al., 2000   
 Type locality. — Bukittingi [Fort de Kock], West Sumatra, Indonesia.   
  Type material. —  Holotype male (ISNB, examined): “ ”, “ Fort de Kock (Sumatra) 920M. 1924 leg. E. Jacobson ” [printed], “ Knisch det. 1925 [printed] Hydraena scabra Orch. [handwritten]”, “coll d’Orchymont” [handwritten], “TYPE” [printed, red], “ A. d’Orchymont det [printed] H. jacobsoni TYPE [handwritten]”, “AEDEAGUS DRAWN BY P.D.PERKINS” [printed]. Paratypes (ISNB): 3 females, same locality data as holotype; 2 females from Lake Ranau (South Sumatra), 1 female from Singkarak (Central Sumatra), 1 female from Palembang (South Sumatra). We have not examined the pygidial sclerites of these seven female paratypes to test their specific assignation.   
 Additional material examined. — SINGAPORE: 3 males, 5 females (NMW, ZRC): Bukit Timah Nature Reserve, coll. H. K. Lua et al., 13 Dec.1995 “NS 214”; 1 male, 1 female (ZRC): same locality, coll. H. K. Lua, 2 Apr.1997 “NS 224”; 1 male, 1 female (ZSM): Bukit Timah, swamp near fish pond, 9 Apr.1997, coll. Balke & Hendrich; 2 females (ZRC): Bukit Timah NR., small stream near entrance (Taban Valley), coll. Balke & Hendrich, 9 Apr.1997; 1 male (ZRC): Botanic Gardens, pond, coll. H. K. Lua, 22 Apr.1997 “NS0227”; 6 males, 6 females (NMW, ZRC): Nee Soon Swamp Forest, coll. D. H. Murphy & C. M. Yang, 16 Apr.1992 “Y790”; 1 female (ZRC): same locality, but coll. K. L. Yeo, 6 May 1992 “424 Y794D”; 1 male (ZRC): Lorong Banir [Nee Soon], coll. H. K. Lua et al., 16 Jun.1995 “NS 191”; 4 exs. (ZRC): Lower Peirce Reservoir, coll. H. K. Lua, 22 Apr.1997 “NS 230a”; 1 female (ZRC): Senoko nr. Sg [River] Sembawang, coll. K. K. P. Lim et al., 10 Feb.1992 “424 Y777A”; 7 exs. (ZRC): same locality and date, but coll. K. K. P. Lim et al. “Y777b”; 1 male, 2 females (ZRC): same locality, but coll. C. M. Yang & B. K. Kung, 12 Mar.1992 “784A”. Additional specimens from Nee Soon Swamp Forest and Senoko are kept in alcohol (ZRC).   
 Diagnosis. — Externally, this species is very similar to H. formula. Body length: 1.25–1.45 mm.   
Terminal segment of maxillary palpi never darkened.  
 Externally, males can be distinguished from H. formula by the curved foretibia, the slightly wider mesoventral process, the unmodified metaventral plaques, and by the tergite X.   
 Male terminal sternite and spiculum (Fig. 10d): Somewhat resembling a contrabass, apically wider than in H. formula; apex more or less truncate, with tiny median projection.   
 Aedeagus (Fig. 10a–c): Somewhat similar to H. formula and H. scabra Orchymont, 1925 (Freitag & Jäch, 2007). Apex of main piece produced into a curved spine, pointing ventrad; one dorsal seta near apical fourth; ventral margin with conspicuous spine-like projection near insertion of left paramere. Distal lobe with spiny apex and short apical flagellum; with long dorsal setiferous appendage near base. Parameres articulately connected with main piece, inserted near middle of main piece; left paramere subtriangular, fringed with long setae along ventral margin (except near apex), and in apical part of dorsal margin; right paramere short and slender, with ventral and apical setae.   
 Females of H. jacobsoni can be distinguished from H. formula by the gonocoxite and by the spermatheca.   
Gonocoxite (Fig. 10e) distinctly transverse, subtrapezoidal; lateral margin distinctly convex subbasally; setae confined to apical area; basal apophyses long; inner plate projecting sublaterally; paired caveae of inner plate connected medially.  
 Female tergite X (Fig. 10f) inconspicuous, very similar to that of H. formula. Hyaline margin excised apically.   
Spermatheca (Fig. 10g –h): Proximal portion crescentic; distal portion cup-shaped.  
Secondary sexual characters: Male foretibia slightly curved. Male mesoventrite more deeply impressed between mesoventral disc and mesoventral process. Male tergite X apically asymmetrically excavate; apex emarginate, corners subacute, right corner slightly longer than left one.  
 Distribution. — Thailand, Malaysia (Perak, Kedah, Sarawak), Singapore (Fig. 15), Indonesia (Sumatra to Lombok).   
In the original description (Orchymont, 1932) this species was also recorded from northern Vietnam (Lac Thô, Hòa Bình Province). However, among the type material (ISNB) there is no specimen from Vietnam (see above).  
In Singapore, this species was collected in the following locations: Bukit Timah Nature Reserve (swamp near fish pond, stream in Taban Valley), Nee Soon Swamp Forest, Lower Peirce Reservoir, Botanic Gardens, and Senoko (natural habitat destroyed).
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 62-65, DOI: 10.5281/zenodo.5351598