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The abdomen of the pseudoscorpion is oval and has a wide junction with the rectangular carapace, the shell-like covering of the head and upper part of the body. The chelicerae, or grasping pincers, are small and are equipped with structures for cleaning the mouthparts. The pedipalps, smaller, pincerlike appendages, have poison glands opening at the tips. On various parts of the body are numerous trichobothria, or sensory hairs, which can sense small air currents. Pseudoscorpions move slowly, holding their pedipalps in front of them. They feed on small arthropods, which they subdue with poison and then tear apart with the chelicerae. Pseudoscorpion respiration occurs through two pairs of spiracles, or openings to the outside, leading to a tracheal system, branching tubes that bring air to the system. The third pair of walking legs has excretory glands near the coxae, or base segments. Pseudoscorpions are from 1 to several millimeters long (0.04 to 0.25 in).
The sexes are similar in appearance. They display a number of complex mating rituals. In some species, the male deposits a spermatophore, or sperm bundle, in the shape of a stalk on the ground. The female is attracted to the stalk chemically, or she may follow a strand of silk laid down by the male. She then positions herself over the spermatophore and takes it into her genital opening. In other species, the male may guide the female to the spermatophore and then position her over it by grasping her pedipalps. He then pushes against her to aid in the uptake of the sperm. The female produces eggs after successful sperm transfer. She makes a nest out of debris and lines it with silk from glands in her chelicerae. The eggs are held in a membranous sac attached to the female, and she gives them nourishment from her ovaries. The young emerge from the sac after shedding their skin, or molting, twice and undergo two more molts before becoming adults, which may take up to a year. From 2 to 50 young may be hatched per brood cycle. Pseudoscorpions generally live two to five years.
Scientific classification: Pseudoscorpions are arthropods in the order Pseudoscorpionida, class Arachnida, which includes spiders, scorpions, ticks, and mites.