Palpigradi

Palpigradi 

an order of very small (to 2 mm) soil-dwelling arachnids. The body is elongated, and the cephalothorax is covered above by three plates. The abdomen has 11 segments and a long tail. The chelicerae are clawed. The pedipalps are fitted for walking, and the front pair of legs serve a tactile function. The arachnids are marked by cutaneous respiration, and most species lack tracheae. The lower surface of the abdomen has vesicles that draw in moisture. The excretory organs are coxal glands.

There are about 25 species, distributed primarily in the Mediterranean region, the Americas (from California to Chile), southeastern Asia, and southern Australia. No species have been encountered in the USSR. The most common species are those of the genus Koenenia. Palpigradi dwell in warm regions with karstic terrain. They live under rocks and descend deep into cracks in the limestone, often falling into caves.