This picture shows the characteristic gill structure of the Rhithrogena genus more clearly than the mature specimens of Rhithrogena impersonata that I collected back in the Midwest. The "suction cup" gill structure is an adaptation to help the nymphs cling tight to rocks in fast water.
Rhithrogena impersonata (Dark Red Quill) Mayfly Nymph from Mongaup Creek in New York
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