Figures: 4, 31, 105, 125, 177, 217
In addition to the Ecdyonurinae characteristics, the following combination of characteristics will identify the genus:
Atopopus are distinctive in appearance because the head capsule is emarginate posterolaterally (as in Fig. 37) and has an extremely thickened anterior margin (Fig. 31), the lamellae on gills 1 are minute, and the posterolateral spines of the abdomen have a wide base (Fig. 105). Atopopus is most similar to, and most closely related to, Thalerosphyrus, but all species of Thalerosphyrus have well developed lamellae on gills 1. Additionally, most species of Thalerosphyrus have long, acutely pointed posterolateral spines on the abdominal segments and sharply pointed supracoxal spurs.
Atopopus males are distinguished by having hindtarsi ~1.5X the length of the hindtibiae (Fig. 125) and by having both the fore- and hindwings with brown staining near the margins (Fig. 177). Other genera may have brown staining between the costa and subcosta or around crossveins, but no other Ecdyonurinae genus has brown staining on the hindwings.
Philippines, Borneo (Fig. 217).