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order name Araneida, or Araneae, a member of a group of arachnids characterized by having six pairs of appendages, including four pairs of legs and two main body parts (the prosoma, or cephalothorax, and the opisthosoma, or abdomen) attached by a narrow stalk.
Spiders are abundant worldwide except in Antarctica and usually occur at elevations from sea level to 5,000 m (16,000 feet). Some 34,000 species of spiders have been described. Most are terrestrial animals. They range in body length from less than 1 mm (0.04 inch) to about 90 mm (3.5 inches). Spiders are predatory and prey mostly on insects.
All spiders have venom glands, but the venoms of only a few (e.g., black widow, brown spider; ) are harmful to humans. There are eight or fewer eyes, always simple rather than compound (i.e., multifaceted). The number and arrangement of these eyes are major considerations in the classification of species. A pair of chelicerae--two-segmented, pincerlike appendages--occur at the front of the prosoma and usually point downward. The end segment of each chelicera is fanglike and is connected to a venom gland. The legs have seven segments. At the tip of the opisthosoma are several fingerlike structures, known as spinnerets, which produce viscous droplets of silk from the silk glands, forming threads.
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