Heptageniidae of the World: Part II. Key to the Genera

Larval Diagnosis

Larvae of all Ecdyonurus, except the simplicioides species group may be diagnosed by the combination of the presence of interfacing setae on the caudal filaments (as in Fig. 102) and large, posteriorly projecting pronotal extensions (Fig. 8). Other Ecdyonurinae genera that may posses pronotal extenstions (i.e. Thalerosphyrus) differ in having simple scattered setae on the ventral surface of the maxillae (as in Fig. 49), as opposed to fimbriate setae (as in Fig. 51), and they lack interfacing setae on the caudal filaments. Larvae of the simplicioides group cannot be differentiated from those of Nixe except on a species by species basis. In North America, the simplicioides group has a western distribution, whereas Nixe are mostly eastern. In central North America, Nixe and E. simplicioides (McDunnough) are sympatric but E. simplicioides differs from Nixe in having the pair of pale spots on the anterior margin of the head capsule separated by a distance subequal to or slightly greater than the distance between the bases of the antennae (Fig. 33), whereas the pale spots in sympatric Nixe are closer together than the bases of the antennae (Fig. 32). Nixe kennedyi (McDunnough) occurs in western North America, but the larvae are unknown. In mature female larvae of Nearctic Ecdyonurus, the eggs have scattered knob terminated coiled threads with either scattered tubercles (Fig. 109) or ridges covered with small granules (Fig. 108). In contrast, all known Nixe have a distinctive meshlike pattern of ridges surrounding the knob terminated coiled threads (Fig. 110).

Adult Diagnosis

Males of Ecdyonurus typically have penes that are somewhat triangular in shape with well-developed lateral sclerites and apical sclerites that extend over the medial surface (Fig. 147). Dorsolateral spines are absent or minute and ventral spines are absent on the penes. Males of the simplicioides group differ in that the penes have ventral spines (as in Figs.144, 163), small dorsolateral spines, and less developed sclerites. Males of the simplicioides group are similar to those of Nixe, but differ in that the titllators are not thickened and denticulate. Males of Leucrocuta and Ecdyogymnurus are also similar to the simplicioides group but differ in having well-developed dorsolateral spines and apical sclerites that distinctly extend dorsally.

North American females can be differentiated from other Ecdyonurinae by the combination of the absence of dark staining on the wings and by having eggs with only small tubercles or ridges on the chorion (Figs. 108-109) that are never arranged in a mesh-like pattern.

Distribution

Holarctic; Oriental (Fig. 225).

Figures