42a (41b). Abdomen with 3 long thread-like caudal filaments and with style-like appendages on

some abdominal segments (Fig.A); mouthparts mandibulate, but often somewhat

retracted into head; body almost always covered with scales; terrestrial [bristletails].…...….. 43

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A

42b. Abdomen with only 2 thread-like caudal filaments or none; if with 3 [mayfly nymphs]

then aquatic; other characters variable...............................................................................………....... 44