1. Gill 7 teardrop shaped and asymmetrical, with posterior (inner) edge somewhat straightened or slightly concave distally, anterior (outer) margin smooth (not serrate) with or without setules (minute setae), and posterior margin serrate, with or without setules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acerpenna pygmaea
Gill 7 spindle shaped and symmetrical, anterior (outer) and posterior (inner) margins serrate and with setules. . . . . . . . . . . . . . . . . . . . . . . . . . . Acerpenna macdunnoughi
[Note: Condition of the gill margin is best studied under compound magnification.]
Key to Ohio Acerpenna Nymph Species