HYDROMETRINAE, Billberg, 1820

Yang, Chang Man & Zettel, Herbert, 2005, Guide To The Aquatic Heteroptera Of Singapore And Peninsular Malaysia. V. Hydrometridae, Raffles Bulletin of Zoology 53 (1), pp. 79-97 : 79-80

SUBFAMILY HYDROMETRINAE

There are four genera in this subfamily: Bacillometra (South America), Chaetometra , Dolichocephalometra (Marquesas Islands) , and the cosmopolitan Hydrometra . The genus Hydrometra is common and widespread in Southeast Asia.

The body length of Hydrometra ranges from 7 to 18 mm. They are usually brownish, dark greenish or blackish in colour. Species of Hydrometra are quite uniform in general structure, the detailed morphology has been studied by Andersen (1982a) and Polhemus & Polhemus (1995). Some characteristics that are important for species identification are mentioned here.

The elongated head is about 1/3 of the body length; eyes are far away from the anterior margin and divide the head into anteocular (AO) and postocular (PO) parts ( Fig. 2 ). The length ratio of the AO: PO is sometimes helpful for identification. Antennae are long and semiflagelliform, about half of the body length. The shape of anteclypeus (or clypeus, Figs. 2 , 12 ) and its anterior margin vary among different species. It is important for species identification as well as for separation of species groups. Most species have rounded, acute or spine-like anterior, others have broadly rounded to almost straight anterior. The broad anteclypeus with truncate or concave anterior margin type is considered as the most plesiomorphic character state ( Andersen 1977, 1982a) and defines a distinct, widely distributed species group. In the Oriental Region, H ydrometra brevitarsus , gilloglyi , heoki and julieni belong to this group. The gular lobe and maxillary plate ( Figs. 2 , 26 , 39 ) are variable among some species, for example, H. carinata has enlarged maxillary plates.

The thorax is shorter than the head, the distinctive pronotal lobe is covered with punctures and the acetabula usually with acetabular pits. The number of pits differs slightly among species. Some brachypterous females of H. longicapitis bear a long tubercle process on the posterior of the pronotal lobe ( Fig. 4), this unusual polymorphism has not been observed in other species ( Andersen, 1992; Polhemus & Polhemus, 1995). The legs of Hydrometra are long and thread-like, and have 3- segmented tarsi with terminal claws. The modification of legs is mainly through length, with the exception of the species group H. maidli-borneensis - annamana that has a row of hairs on the hind femora of the male.

The wing venation is reduced as compared to most other semiaquatic bugs. In the macropterous (mapt) morph the wings are long, covering most of the abdominal tergites. In the brachypterous (brpt) morph the wings are reduced to narrow straps, which hardly extend onto the surface of the abdomen. In apterous (apt) (or micropterous) morph the wings are either completely covered by the pronotal lobe, or just visible as very tiny pads behind its hind margin. Information on wing morphs is often a valuable hint for recognition of species. In general, Hydrometra species usually occur in two different morphs. Most species have a brachypterous and a macropterous morph. Some species are only known for one morph, an apterous (or micropterous) or a macropterous morph. A few species are only known in brachypterous morph, but the occurrence of macropterous specimens has to be expected. In the key we mention the more common morph first, followed by the less common, e.g., “mapt or brpt”. If one morph occurs rarely, it is put in parenthesis, e.g., “mapt (or brpt)”.

The abdomen ( Figs. 3 , 4) is relatively long, covered with short and fine pubescence, and some long setae. The mediotergites are narrow, and the width to length ratio is useful in separating some closed related species. Laterotergites (connexiva or paratergites) of some species carry long erected setae ( Figs. 23, 24 , 33 , 51 ). Sternite 7 of the male is modified. Some are transversely concave and dispersed with long setae ( Fig. 40 ); some with patches of short hairs or with a pair of clustered set of long setae ( Figs. 14, 18 ), or modified with thorn-like, or spine-like process ( Figs. 29 , 50 , 80 , 88), whilst H. longicapitis has a pair of very distinct fleshy tubercle processes on the anterior of sternite 7 ( Fig. 66 ). Segment 8 of male is usually not modified, but some species have slight depression or paired cluster of setae ventrolaterally ( Figs. 36 , 45, 47 ). The posterodorsal corners are usually rounded, but a few species have distincted outwarded process because of the expanded wing-like structure of the pygophore (S9) ( Fig. 62 ). The sternite 7 of the female is not modified, but its length and shape, as well as the terminal process of tergite 8 are useful characters for species identification.

Figures

Fig. 2. Head of Hydrometra (from Polhemus & Polhemus, 1995). Abbreviations: AC, anteclypeus; AO, anteocular distance; GL, gular lobe; MXP, maxillary plate; MDP, mandibular plate; PO, postocular distance.

Figs. 12-19: 12-15: Hydrometa annamana Hungerford & Evans; 12. Apex of head, dorsal view showing anteclypeus (AC); 13. Male terminal abdomen, lateral view; 14. Male terminal abdomen, ventral view; 15. Female terminal abdomen, lateral view. 16-19: Hydrometra borneensis Zettel & Yang; 16. Apex of head, dorsal view showing anteclypeus; 17. Male terminal abdomen, lateral view; 18. Male terminal abdomen, ventral view; 19. Female terminal abdomen, lateral view.

Figs. 20-27: 20-24: Hydrometra brevitarsus Zettel & Yang; 20. Apex of head, dorsal view showing anteclypeus; 21. Male terminal abdomen, lateral view; 22. Male terminal abdomen, ventral view; 23. Female terminal abdomen, dorsal view; 24. Female terminal abdomen, lateral view. 25-27: Hydrometra carinata Polhemus & Polhemus; 25. Apex of head, dorsal view showing anteclypeus; 26. Head, lateral view (AC, anteclypeus; Gl, gular lobe; MXP, maxillary plate); 27. Female terminal abdomen, lateral view.

Figs. 36-43: 36-37: Hydrometra gilloglyi Polhemus & Polhemus; 36. Male terminal abdomen, vental view; 37. Female terminal abdomen, lateral view, note the posterior-median protrusion of sternite 7. 38-42: Hydrometra greeni Kirkaldy; 38. Apex of head, dorsal view showing anteclypeus; 39. Head, lateral view (Gl, gular lobe; MXP, maxillary plate); 40. Male terminal abdomen, lateral view; 41. Male terminal abdomen, ventral view; 42. Female terminal abdomen, lateral view; 43. Hydrometra heoki heoki Zettel & Yang, apex of head, dorsal view showing anteclypeus.

Fig. 3. Hydrometra longicapitis Torre-Bueno, brachypterous male with appendages removed, dorsal view. Abbreviations: L, laterotergite; PT8, posterior process of segment 8 (Sg8); T, tergite; W, wing.

Figs. 28-35: 28-29: Hydrometra carinata Polhemus & Polhemus, male terminal abdomen; 28. lateral view; 29. cluster of spines on sternite 7. 30-33: Hydrometra cracens Polhemus & Polhemus; 30. Apex of head, dorsal view showing anteclypeus; 31. Male terminal abdomen, lateral view; 32. Male terminal abdomen, ventral view; 33. Female terminal abdomen, lateral view. 34-35: Hydrometra gilloglyi Polhemus & Polhemus; 34. Apex of head, dorsal view showing anteclypeus; 35. Male terminal abdomen, lateral view.

Figs. 44-51: 44-46: Hydrometra heoki heoki Zettel & Yang; 44. Male terminal abdomen, lateral view; 45. Male terminal abdomen, ventral view; 46. Female terminal abdomen, lateral view; 47. Hydrometra heoki paya Zettel & Yang, male termainal abdomen, ventral view; 48-51: Hydrometra jaczewskii Lundblad. 48. Apex of head, dorsal view showing anteclypeus; 49. Male terminal abdomen, lateral view; 50. Male, cluster of setae on sternite 7; 51. Female terminal abdomen, lateral view.

Figs. 76-83: 76-77: Hydrometra mindoroensis J. Polhemus; 76. Male terminal abdomen, ventral view; 77. Female terminal abdomen, lateral view. 78-80: Hydrometra okinawana Drake; 78. Apex of head, dorsal view showing anteclypeus; 79. Male terminal abdomen, lateral view. 80. Male, cluster of tightly thorns on sternite 7; 81-83: Hydrometra orientalis Lundblad; 81. Apex of head, dorsal view showing anteclypeus. 82. Male terminal abdomen, lateral view; 83. Male terminal abdomen, ventral view.

Figs. 60-67: 60-64: Hydrometra lineata Eschscholtz; 60. Apex of head, dorsal view showing anteclypeus; 61. Male terminal abdomen, lateral view; 62. Male terminal abdomen, ventral view; 63. Female terminal abdomen, dorsal view; 64. Female terminal abdomen, lateral view. 65-67: Hydrometra longicapitis Torre-Bueno; 65. Apex of head, dorsal view showing anteclypeus; 66. Male terminal abdomen, lateral view; 67. Male terminal abdomen, ventral view.