(also Atelocerata), a subphylum of terrestrial or secondarily aquatic arthropods characterized by a head clearly distinguished from the trunk, with one pair of antennae and three pairs of mandibles. Respiration is usually tracheal and sometimes cutaneous, although insect larvae secondarily adapted to life in water breathe by means of tracheal gills, outgrowths of the body walls to which appendages of the tracheal system extend. Myriapods and insects belong to the Tracheata. The term “Tracheata” is not very apt because forms with tracheal respiration are also found in other subphyla of arthropods, for example, Chelicerata.