Unlike insects, spiders have four pairs of legs.
Spiders are arthropods, invertebrates with an exoskeleton of chitin and articulated legs. Unlike other arthropods such as insects, spiders don't have a separate head and thorax or antennae, but a fused cephalothorax that also contains two pedipalps or palps. In addition to the cephalothorax and pedipalps, other body parts of a spider include chelicerae, an abdomen and four pairs of legs.
Cephalothorax
Located in the anterior part of the body, the cephalothorax or prosoma contain vital organs, such as the brain and part of the digestive system. The cephalothorax also contains important appendages or body extensions, such as pedipalps and chelicerae. All eight legs that characterize all spider species are attached to the cephalothorax.
Abdomen
Also called the opisthosoma, the abdomen of spiders is often round and large and contains organs of the respiratory and circulatory systems. Located in the posterior part of the body, the abdomen also contains the spinnerets, which are the organs that produce the silk for web-making.
Legs
An important characteristic that differentiates spiders from insects is the number of legs. All spiders have four pairs of legs, each of them containing seven segments: tarsus, metatarsus, tibia, patella, femur, trochanter and coxa. Some species, such as the wolf spider, have hairy legs and claws, which help them hang onto their silk threads.
Pedipalps and Chelicerae
Located on both sides of the cephalothorax, pedipalps are two elongated organs similar to antennae which the spider uses to explore the environment and hold onto prey when eating. Chelicerae are two hook-like organs found in the mouth of a spider which are used to inject venom when biting or hunting for prey.
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