Pseudoscorpionida
| Pseudoscorpions (false scorpions) Temporal range: 380–0 Ma Devonian to Recent |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Arachnida |
| Order: |
Pseudoscorpiones Haeckel, 1866 |
| Superfamilies | |
A pseudoscorpion, also known as a false scorpion or book scorpion, is an arachnid belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida.
Pseudoscorpions are generally beneficial to humans since they prey on clothes moth larvae, carpet beetle larvae, booklice, ants, mites, and small flies. They are tiny and inoffensive, and are rarely seen due to their small size, despite being common in many environments.
Pseudoscorpions belong to the arachnida class. They are small arachnids with a flat, pear-shaped body and pincers that resemble those of scorpions. They usually range from 2 to 8 millimetres (0.08 to 0.31 in) in length. The largest known species is Garypus titanius of Ascension Island at up to 12 mm (0.5 in). Range is generally smaller at an average of 3 mm (0.1 in).
The abdomen, known as the opisthosoma, is made up of twelve segments, each protected by plates (called tergites above and sternites below) made of chitin. The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions (the fact that they look exactly like scorpions, aside from not having a stinger tail, is the source of the name "Pseudoscorpion"). The color of the body can be yellowish-tan to dark-brown, with the paired claws often a contrasting color. They may have two, four or no eyes.
A pseudoscorpion has eight legs with five to seven segments; the number of fused segments is used to distinguish families and genera. They have two very long pedipalps with palpal chelae (pincers) which strongly resemble the pincers found on a scorpion.
The pedipalps generally consist of an immobile "hand" and "finger", with a separate movable finger controlled by an adductor muscle. A venom gland and duct are usually located in the mobile finger; the venom is used to capture and immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions pour a mildly corrosive fluid over the prey, then ingest the liquefied remains.
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