Guide To The Aquatic Heteroptera Of Singapore And Peninsular Malaysia: Vii. Family Helotrephidae Author Zettel, Herbert Author ek, Miroslav Papá Author Kovac, Damir text Raffles Bulletin of Zoology 2011 2011-08-31 59 2 171 179 journal article 10.5281/zenodo.10107176 2345-7600 10107176 Key to the species of Hydrotrephes 1 Metasternal carina long, with straight ventral margin; abdominal sternite 4 with small medial tubercle ( Fig. 22 ). Aedeagus simple ( Figs. 64 ). Southern Thailand . Hydrotrephes mirus group ...... ............................................................. [ Hydrotrephes mixtus ] – Metasternal carina short, with convex ventral margin; abdominal sternite 4 without medial tubercle (e.g., Fig. 23 ). Aedeagus modified, posteriorly or postero-subapically with process or tooth ( Figs. 65, 68, 71, 74 ) .................................................. 2 2 Subgenital plate of female with triangular apical lamella ( Figs. 60, 61 ). Hind margin of aedeagus with long process ( Figs. 65, 68 ). Right paramere stout, with broad apex ( Figs. 67, 70 ). Hydrotrephes bouvieri group ............................................... 3 – Subgenital plate of female distally either with broad lobe or with long and slender process ( Figs. 62, 63 ). Hind margin of aedeagus with short tooth ( Figs. 71, 74 ). Right paramere slender, with pointed apex ( Figs. 73, 76 ). Hydrotrephes martini group ............................................................................................... 4 3 Subgenital plate of female with small distal lamina ( Fig. 60 ) Aedeagus with triangular apex and curved posterior process ( Fig. 65 ). Southern Thailand ................ [ Hydrotrephes sitesi ] – Subgenital plate of female with large distal lamina ( Fig. 61 ). Aedeagus with elongate apex and straight posterior process ( Fig. 68 ). Southern Thailand ........ [ Hydrotrephes maculatus ] 4 Body length 1.9–2.2 mm, cephalonotum width 1.3–1.5 mm. Subgenital plate of female distally with broad lobe ( Fig. 63 ). Aedeagus with roundish apex ( Fig. 71 ) ................................... .................................................... Hydrotrephes langkawicus – Body length 2.6–2.8 mm, cephalonotum width 1.8–2.1 mm. Subgenital plate of female distally with long and slender process ( Fig. 62 ). Aedeagus with elongate apex ( Fig. 74 ). ...................................................... Hydrotrephes benomensis