An order of small to medium-sized wingless insects, sometimes known as ‘two-pronged bristletails’, with elongated bodies, prominent paired tail-like cerci, and slender paired antennae. There are some 800 known species, typically 2–5 mm long, exceptionally reaching 50 mm. They lack eyes, have partially concealed mouthparts, and are found in dark humid places, for example in soil or under bark, living mostly on decaying vegetation, although some species are predators. The number of body segments is fixed during development, and moulting continues throughout life. Although some authorities place the Diplura in the subclass Apterygota, with the other wingless insects, others regard them as a separate class within the subphylum Hexapoda.