Gestroiella, Montandon, 1897

Polhemus, Dan A. & Polhemus, John T., 2013, Guide To The Aquatic Heteroptera Of Singapore And Peninsular Malaysia. Xi. Infraorder Nepomorpha- Families Naucoridae And Aphelocheiridae, Raffles Bulletin of Zoology 61 (2), pp. 665-686 : 680

Genus GESTROIELLA Montandon, 1897

Discussion. — Members of this genus are distinctive within the regional naucorid assemblage by having the body broadly oval to nearly round ( Fig. 36 ), and strongly dorsoventally flattened; a posteroventral folding of the preclypeal head; the retraction of the labrum, rostrum and antennae into cavities on the underside of the head; and the presence of large pads of bristle-like setae ventroapically on the middle and hind tibiae. The pronotum is very broad, with the posterior width approximately 2× the width of the head, the anterolateral angles of the pronotum are simple, not forming cup-shaped depressions ventrally at the apices as in the related Indochinese genus Cheirochela , and the posterolateral angles are acute but not spinose ( Fig. 36 ). The hemelytra of brachypterous forms are long, with the apices angulate, reaching to or surpassing abdominal tergite VI ( Fig. 36 ), and the abdominal and thoracic venter have a fine pile of short, closely appressed hydrofuge hairs. The male phallotheca and parameres are symmetrical, with the paramere stout basally, then suddenly narrowing on the distal half to form a tapering arm, the apex of which is weakly notched ( Fig. 38 ).

Range. — Described from Thailand (D. Polhemus et al., 2008), and to date known only from that country.

Discussion. — Members of the genus Gestroiella have a unique body shape that is immediately recognisable among extant Naucoridae ( Fig. 36 ). The only member of this genus to occur near the region under study, Gestroiella siamensis , occupies an elongate north-to-south range extending from the southern Shan Plateau southward through the entire mountain spine of the Thai-Burmese border area to the Isthmus of Kra (see Fig. 35 in D. Polhemus et al., 2008), and as such may occur in the mountain streams of far northern Peninsular Malaysia. This species has been collected in clear, rockybottomed streams with a wide range of current velocities, but is absent from sluggish or stagnant reaches.

Figures

Fig. 36. Gestroiella siamensis D. Polhemus, J. Polhemus & Sites, male, dorsal habitus, specimen from Thailand, Songkla Prov., Ton Nga Chang (Young Sohn illustration).

Figs. 37–39. Gestroiella siamensis D. Polhemus, J. Polhemus & Sites, structural details, specimen from Thailand, Thailand, Songkla Prov., Ton Nga Chang. 37. Female terminal abdomen, ventral view, showing shape of subgenital plate. 38. Male left paramere. 39. Medial process of male phallotheca.

Figs. 34, 35. Heleocoris species, male left abdominal paratergites. 34. Heleocoris malayensis, new species, specimen from Malaysia, Terengganu, Sungai Brang. 35. Heleocoris ovatus Montandon, specimen from Vietnam, Lam Dong Prov., Pongour Falls.