scorpion, any arachnid of the order Scorpionida with a hollow poisonous stinger at the tip of the tail. Scorpions vary from about 1/2 in. to about 6 in. (1–15 cm) long; most are from 1 to 3 in. (2.5–7.6 cm) long. They are predominantly tropical or subtropical, but some species live in temperate regions. During the day they hide in crevices or under objects, emerging at night to feed, mostly on other arthropods. The body is composed of a prosoma (head) covered by a solid protective covering, or carapace, and a segmented opisthosoma (body) divided into a broader mesosoma and a narrower metasoma, which ends in a sting. There are six pairs of appendages located on the prosoma: short, pincerlike appendages called chelicera, which are used to tear up food for swallowing; large appendages called pedipalps, equipped with powerful pincers used to grasp prey (which is then immobilized by stinging if necessary); and four pairs of walking legs. The first segment of the opisthosoma has vestigial appendages in the form of a genital opening (operculum), and the second segment bears unique, comblike sensory appendages known as pectines. The next four opisthosomal segments each bear a pair of respiratory structures known as book lungs , which open into the body by way of a hole, or spiracle. The metasoma is carried high in the air, in preparation for a quick stinging thrust. Although scorpion stings are painful, they are not usually dangerous to humans. Exceptions are the greatly feared scorpion Androctonus australis of the Sahara Desert, whose sting causes death in 6 to 7 hr if the victim is not treated with antivenin, and several species of the genus Centruroides, found in Mexico, which have been responsible for the deaths of a number of persons, mostly children. The scorpion neurotoxin causes convulsions; death results from respiratory or cardiac failure. Complex courtship rituals precede mating. The young scorpions are born alive and are carried for a time by the mother, leaving her after the first molt. About a year is required to reach maturity. Scorpions are classified in the phylum Arthropoda , class Arachnida, order Scorpionida.
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