Symphyla are small, cryptic myriapods without eyes and without pigment.[4] The body is soft and generally 2 to 10 millimetres (0.08 to 0.4 in) long, divided into two body regions: head and trunk. An exceptional size is reached in Hanseniella magna, which attains lengths of 25 to 30 mm (1.0 to 1.2 in).[5]
The head has long, segmented antennae, a postantennal organ, three pairs of mouthparts: mandibles, the long first maxillae, and the second pair of maxillae which are fused to form the lower lip or labium of the mouth. Disc-like organs of Tömösváry, which probably sense vibrations, are attached to the base of the antennae, as they are in centipedes