Epigastric furrow

The anatomy of spiders includes many characteristics shared with other arachnids. These characteristics include bodies divided into two tagmata (sections or segments), eight jointed legs, no wings or antennae, the presence of chelicerae and pedipalps, simple eyes, and an exoskeleton, which is periodically shed.

Spiders also have several adaptations that distinguish them from other arachnids. All spiders are capable of producing silk of various types, which many species use to build webs to ensnare prey. Most spiders possess venom, which is injected into prey (or defensively, when the spider feels threatened) through the fangs of the chelicerae. Male spiders have specialized pedipalps that are used to transfer sperm to the female during mating. Many species of spiders exhibit a great deal of sexual dimorphism.

Spiders, unlike insects, have only two main body parts (tagmata) instead of three: a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (also called an opisthosoma). The exception to this rule are the assassin spiders (family Archaeidae), whose cephalothorax is divided into two parts by an elongated "neck". In the majority of spiders, the abdomen is not externally segmented. The exception is the Liphistiidae, a basal family, which retains this more primitive character; hence they are sometimes called segmented spiders. The abdomen and cephalothorax are connected by a thin waist called the pedicel. Unlike insects, spiders have an endoskeleton in addition to their exoskeleton.

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