47a (46b). Having 3 caudal filaments; tarsi with 1 claw; gills located on lateral margins of

abdominal terga (= dorsal plates or sclerites) and usually leaflike or plate-like

(Figs.A-C) [mayfly nymphs].........................................................................................Ephemeroptera

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A B C

47b. With 2 caudal filaments; tarsi with 2 claws; gills mostly present, somewhat fingerlike,

usually located on underside of thorax (Figs.A-D) [stonefly nymphs]................................Plecoptera