Adults possess 15 pairs of very long legs that become progressively longer caudally; antennae very long and whip-like, consisting of two basal articles and a long flagellum with hundreds of very short articles; head hemispherical, with two compound eyes that differ structurally from those of insects; trunk not dorsoventrally flattened (adults have 15 sterna but only 7 large terga because of tergal fusion)
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