Ranatra biroi, Lundblad, 1933

Tran, A. D. & Zettel, H., 2021, Taxonomy of the Ranatra biroi group sensu Lansbury, 1972 (Nepomorpha: Nepidae), with descriptions of two new species, Raffles Bulletin of Zoology 69, pp. 507-521 : 508

Ranatra biroi group sensu Lansbury, 1972

Remarks. Species of the R. biroi group can be recognised by the combination of the following characteristics: small size, body length not greater than 33.0 mm (males 17.5–30.0 mm, females 18.7–33.0 mm); siphon length about 0.60–1.05× body length, depending on species; vertex generally higher than eye in lateral view (except R. biroi Lundblad, 1933 ) and usually with very low tubercle (in some species without tubercle); eye width in dorsal view about 0.9–1.5× interocular width; anterior pronotal length about 1.3–1.8× posterior pronotal length; slender fore femur, with two ventral teeth situated at ca. distal 0.4 of femoral length, without pre-apical tooth; posterior margin of metasternum usually convex (in some species straight or slightly emarginated); operculum of female not extending beyond apex of connexivum (modified from Lansbury, 1972).

The R. biroi group shares many characteristics with the R. filiformis group. According to Lansbury (1972), the only discriminating character is eye width (in dorsal view). Species of the R. filiformis group have smaller eyes; eye width is 0.65–0.98 times of interocular width. However, this character is not completely discrete. Whereas most species of the R. biroi group have eye width at least equal to interocular width (up to 1.3 times), the eye width of R. nieseri Tran & Nguyen, 2016 , ranges between 0.9 and 1.1 times of interocular width. Until further molecular data become available for a phylogenetic approach in the evaluation of this classification, we follow Lansbury’s (1972) classification and treat them as separate groups.

Species of the R. biroi group are highly similar to each other, with very few characters to separate them. The most reliable character is the structure of the paramere. Other characters, e.g., the posterior margin of the metasternum, the relative widths of the mesosternum between the middle coxae and of the metasternum between the hind coxae, and the length of the hind femur, are useful to provisionally separate species, but should be used in combination with the parameres. Thus, identification of species is reliable only for male specimens, and females have to be associated with identifiable males.