Acari: Morphology & Physiology
Mites do not really show the typical cephalothorax and abdomen seen in other arachnids. By contrast, their main division of the body is into the gnathosoma, which bears the mouthparts and pedipalps, and the rest of the body, or idiosoma. Different groups may show further patterns of division. In some groups there is a split between the second and third pair of legs, in others the whole body behind the gnathosoma forms a single sclerotized unit. Mites hatch with a hexapodal (six-legged) larva; the subsequent instars having the full complement of eight legs. Median or lateral eyes may be present, but some groups are completely blind and various types of setae are important sensory organs. Respiration is through trachea and the place where the trachea open is an important diagnostic character for some of the major groups, e.g. Prostigmata or Mesostigmata.