The Pseudoscorpiones is a group of more than 3000 known species of small arachnids that bear a pair of chelate (claw-like) pedipalps, a pair of two-segmented chelicerae, four pairs of legs, and an ovate abdomen. Pseudoscorpions superficially resemble small scorpions, but they lack the elongate tail (metasoma) and sting. The pseudoscorpions are believed to be most closely related to the sun spiders (Solifugae), with which they share many morphological similarities. (Harvey 2011)
Pseudoscorpions can be found in virtually all terrestrial habitats, but are most common in leaf litter, in soil, and under the bark of trees and logs. They are frequently found in caves and many species occur along seashores. They are generally quite small, with adults ranging from around 0.5 to 5 mm in length; however, some species may exceed 1 cm. Pseudoscorpions are typically free-living, solitary predators of other tiny invertebrates. Many pseudoscorpions have venom glands within the pedipalpal fingers, making them the only venom-producing arachnids other than spiders and scorpions. (Murienne et al. 2008 and references therein)
Pseudoscorpions transfer sperm in packages attached to a spermatophore, which is produced from the male’s gonopore and attached to the substrate. Males of most pseudoscorpion families that have been studied simply deposit a spermatophore without any courtship -- and even without the presence of a female. A female subsequently somehow finds the spermatophore and draws the sperm packet into her gonopore. Serianus males deposit a spermatophore in the presence of a female, but there is no physical contact between the sexes. In one branch of the pseudoscorpion family tree, however, there is an elaborate mating dance in which males actively court females, touching and moving them and culminating with the male grasping the female with his pedipalps and depositing a spermatophore on the substrate, then guiding her over the spermatophore, which she draws into her gonopore. (Harvey 2011)
Pseudoscorpion eggs mature internally and the embryos are deposited into a brood-sac attached to the gonopore. The embryos mature until the protonymphs emerge from the brood-sac. They remain with the female for a short time and eventually disperse for a solitary existence.There are four post-embryonic stages: protonymph, deutonymph, tritonymph and adult. The nymphal stages are generally free-living, although the protonymphs of some species are immobile. Many pseudoscorpions build a small silken chamber in which to moult, develop their brood-sac, or shelter themselves. (Harvey 2011)
Del-Claro and Tizo-Pedroso (2009) reviewed the occurrence of sociality in pseudoscorpions (extended parental care, division of labor, cooperative breeding and feeding).
Individuals of some pseudoscorpion species may use their pedipalps to attach themselves to other organisms such as other arachnids, insects, mammals, or birds, which may facilitate transport to different habitats. Some are obligate commensals (i.e., benefiting from their association without harming the host, as a parasite would), spending their entire life cycle, for example, in the nests or fur of mammals (e.g. many species of Lasiochernes and Megachernes). Others form associations with flying insects, attaching themselves to legs, other body parts or, sometimes, under the elytra of beetles. Dozens of species have been collected from birds' nests (Turienzo et al. 2010). (Murienne et al. 2008 and references therein; Harvey 2011)
In addition to the authoritative Pseudoscorpions of the World website, some regions have excellent online resources available for those interested in learning more about pseudoscorpions. Examples of valuable online resources include The Pseudoscorpions of Northern and Central Europe, The UK (and Ireland) Pseudoscorpion Recording Scheme, and Photographic Key to the Pseudoscorpions of Canada and the Adjacent USA.
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