Key to males of South American Rheotanytarsus Thienemann & Bause species

(adapted from Andersen & Kyerematen 2001)

1. Median volsella with apical setiform lamellae fused into a plate; wing length <2 mm ............................... 2

1’. Median volsella with apical setiform lamellae not fused into a plate; wing length> 2 mm ............................ 4

2. Median volsella with rounded apical plate.................................................................. 3

2´. Median volsella with distinct petal-like apical plate. (Andersen & Kyerematen 2001, Figures 9–12)..................................................................................................... R. pelus (Roback, 1960)

3. Superior volsella somewhat oval, about the same size as median volsella; wing length about 1.75 mm. (Reiss 1972, Figure 12)............................................................................. R. lamellatus Reiss, 1972

3´. Superior volsella subtriangular, shorter than median volsella; wing length about 1.10 mm. (Andersen & Kyerematen 2001, Figures 1 –8)................................................. R. pantanalensis Andersen & Kyerematen, 2001

4. Median volsella distinctly longer than superior volsella; gonostylus broadest basally, with abruptly tapered apical half. (Reiss 1972, Figure 11).................................................................... R. globosus Reiss, 1972

4´. Median volsella about the same size as the superior volsella; gonostylus broadest subbasally, evenly tapering toward apex. (Figure 1)............................................................................... R. amaru sp. n.