An order of tiny wingless insects that live in soil and leaf litter. There are about 800 known species. The slender elongate adults are usually 0.5 to 2.5 mm long and lack eyes and antennae; the front pair of legs are held forwards as sensors. The mouthparts, which are largely entognathous (concealed within folds), are adapted for feeding on decaying organic matter. The young resemble the adults, but three segments are added to the end of the abdomen during development. The relationship of proturans to other arthropod groups is controversial. Although some authorities place them in the subclass Apterygota with the other wingless insects, other authors regard the Protura as a separate class within the superclass Hexapoda, most closely affiliated to the Collembola.