Flightless insects with ectognathous mouth parts (externally visible as compared to entognathous mouth parts of the Diplura, Protura and Collembola which are sunk into the head and thus not imediately visible). They have long filiform antennae with as many as, or more than 30 segments. The abdomen has eleven segments generally ending in three 'tails' consisting of two cerci and a telson. They are commonly represented by the Silverfish and the firebrats.
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