This specimen is interesting because Heptagenia pulla
has not been reported from Washington or neighboring states (Saskatchewan is the closest), yet the distinctive key characteristics are clear.
It keys to the genus Heptagenia
because the tarsal claw
has a single basal
tooth, and the gills on segment 7 have fibrils
For the species key:
1. The left mandible
is planate (fairly straight-edged) whereas the right mandible
is angulate (has one sharp turn on the edge).
2. The labrum
is much wider than long.
3. There's a thin light-colored streak lateral
to the eye on the head.