Gestroiella siamensis D. Polhemus, J. Polhemus & Sites, 2008

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 : 680-681

Gestroiella siamensis D. Polhemus, J. Polhemus & Sites, 2008

Figs. 36–39

Gestroiella siamensis, D. Polhemus, J. Polhemus & Sites, 2008: 275

Diagnosis. — This the smallest species in the genus, with a body length of 12.8–14.4 mm. The dorsomedial process of the male genital capsule is broadly triangular ( Fig. 39 ), and the lateral spines of abdominal segments III and IV are relatively small. In males, the posterior margin of abdominal sternum VI is distinctly convex in the middle, and the opposable surfaces of the profemur and tibia are evenly arcuate, rather than having an anteriorly bowed profemur with a gap between it and the protibia as in other members of the genus. The male phallotheca is abruptly narrowed beyond the tips of the parameres, the parameres themselves are relatively slender ( Fig. 38 ), and a mat of dark hairs is present on the phallobase. The female subgenital plate is weakly notched apicomedially ( Fig. 37 ).

onto the metasternum, with segment III very elongated; the tarsi, which are 3-segmented, with the fore tarsi articulated and not fused to fore femur as in Naucoridae ; the persistent dorsal abdominal scent glands in adults; and the abdominal spiracles, which are surrounded by rosettes, this latter character diagnostic for the family. The combination of a long rostrum, long antennae, and abdominal spiracular rosettes is distinctive unique within the Nepomorpha (see Fig. 40, depicting the macropterous form of A. pallens Horváth from New Guinea as an exemplar of this family). Useful characters for separating individual species include the male genitalia ( Figs. 43 , 51 , 55 , 58, 59 ), female subgenital plate ( Figs. 44 , 50 , 57 ), and shape of the proacetabula ( Figs. 46 , 52 , 56 ).

Aphelocheirus species are inhabitants of rocky upland streams, where their use of plastron respiration, associated with the development of the spiracular rosettes, allows them to stay submerged underwater for an indefinite period of time. Individuals are most abundant in areas of mixed gravel and cobble substrate swept by moderate current (D. Polhemus & J. Polhemus, 1989). Such habitats are generally absent in Singapore, but are by contrast extensive in the mountains of Peninsular Malaysia, where representatives of both subgenera currently recognised in the genus, Aphelocheirus and Micraphelocheirus , are known to occur, and it is likely that the current aphelocheirid fauna of this area is underestimated. No species of Aphelocheirus has yet been recorded from Singapore, and the genus is unlikely to occur there given the general absence of suitable rocky streams on the island.

Following the monograph of D. Polhemus & J. Polhemus (1989), which established a firm taxonomic foundation for the genus in tropical Asia, a large number of additional species were described from this region (J. Polhemus, 1989; Chen & Nieser, 1991; D. Polhemus, 1994; Liu & Zheng, 1994; Sites et al., 1997; Zettel, 1998, 1999, 2000, 2001; Nieser et al., 2004; Sites, 2005; Sites & Zettel, 2005; Zettel & Papáček, 2006; Liu & Ding, 2005; Thirumalai, 2008; Zettel et al., 2008; Zettel & Tran, 2009; Zettel & Pangantihon, 2010). As a result, the genus currently contains 92 species worldwide (exclusive of subspecies), with the vast majority of the species added since 1989 having come from tropical Asia. This rush of new taxonomic work was not accompanied by any synthetic review or supplementary monograph, leading to a rather confusing situation for non-specialists at the present time.

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.41–46.Aphelocheirus (Aphelocheirus) femoratus D. Polhemus & J. Polhemus, structural details, specimens from Malaysia, Pahang, Cameron Highlands. 41. Brachypterous male, dorsal habitus. 42. Macropterous male, dorsal habitus. 43. Male parameres and phallotheca. 44. Female subgenital plate. 45. Male hind femur, ventral view. 46. Proacetabula.

Figs. 47–52.Aphelocheirus (Aphelocheirus) grik D. Polhemus & J. Polhemus, structural details. 47. Brachypterous male, dorsal habitus, Malaysia, Perak, Grik. 48. Macropterous female, dorsal habitus, specimen from Thailand, Chiang Mai Prov.. Mae Ping River. 49. Male ventral abdomen, showing tab on abdominal ventrite IV. 50. Female subgenital plate. 51. Male parameres and phallotheca. 52. Proacetabula.

Figs.53–57.Aphelocheirus (Aphelocheirus) malayanus D.Polhemus & J. Polhemus, structural details. 53. Brachypterous male, dorsal habitus, specimen from Malaysia, Perak, near Jeli. 54. Macropterous female, dorsal habitus, specimen from Malaysia, Pahang, Cameron Highlands. 55. Male parameres and phallotheca. 56. Proacetabula. 57. Female subgenital plate.

Figs. 58, 59. Aphelocheirus (Micraphelocheirus) malayensis Zettel & Papáček, male parameres. 58. Left paramere. 59. Right paramere (after Zettel & Papáček 2006).