cephalothorax

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cephalothorax

zoology

Also known as: prosoma

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Last updated

June 24, 2026

Quick Summary

The cephalothorax, also known as the prosoma, is a primary body division in arachnids and some crustaceans. It is formed by the fusion of the head and thorax. In arachnids, this region is covered dorsally by a carapace and houses the mouth, eyes, and appendages, including the chelicerae (pincers or fangs), pedipalps (sensory or manipulative appendages), and four pairs of walking legs. The muscles of the cephalothorax are well-developed, supporting movement. In contrast to the cephalothorax, the abdomen (opisthosoma) is the posterior body section and typically has reduced musculature. While some arachnids have a distinct separation between these two body parts, others, like mites and ticks, have a body that forms a single region.1234

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arachnid
Body and appendages
…into two distinct regions: the cephalothorax, or prosoma, and the abdomen, or opisthosoma. The sternites (ventral plates) of the lower surface of the body show more variation than do the tergites (dorsal plates). The arachnids have simple (as opposed to compound) eyes.
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…into two distinct regions: the cephalothorax, or prosoma, and the abdomen, or opisthosoma. The sternites (ventral plates) of the lower surface of the body show more variation than do the tergites (dorsal plates). The arachnids have simple (as opposed to compound) eyes.
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decapod
…often referred to as the cephalothorax. A pair of appendages is attached to each somite. The first two pairs, the first and second antennae, consist of a segmented stalk and flagella, and serve such sensory functions as olfaction, touch, and balance. The remaining three head appendages are either the crushing…
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…often referred to as the cephalothorax. A pair of appendages is attached to each somite. The first two pairs, the first and second antennae, consist of a segmented stalk and flagella, and serve such sensory functions as olfaction, touch, and balance. The remaining three head appendages are either the crushing…
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horseshoe crab
Natural history
…hinged together: a broad horseshoe-shaped cephalothorax; a much smaller, segmented abdomen; and a long, sharp tail-spine, or telson. The smoothly arched upper surface of the cephalothorax has a pair of lateral compound eyes and a much smaller median pair of eyes that respond to ultraviolet light. Underneath, the cephalothorax bears…
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…hinged together: a broad horseshoe-shaped cephalothorax; a much smaller, segmented abdomen; and a long, sharp tail-spine, or telson. The smoothly arched upper surface of the cephalothorax has a pair of lateral compound eyes and a much smaller median pair of eyes that respond to ultraviolet light. Underneath, the cephalothorax bears…
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scorpion
External features
…front to rear, are the prosoma, the mesosoma, and the metasoma. The mesosoma and the metasoma together form the abdomen, or opisthosoma. The prosoma has six segments, each with a pair of appendages. The three-segmented chelicerae that arise from the first segment are pincerlike (chelate) and serve to masticate food.…
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…front to rear, are the prosoma, the mesosoma, and the metasoma. The mesosoma and the metasoma together form the abdomen, or opisthosoma. The prosoma has six segments, each with a pair of appendages. The three-segmented chelicerae that arise from the first segment are pincerlike (chelate) and serve to masticate food.…
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spider
External features
…divided into two parts, the cephalothorax (prosoma) and the abdomen (opisthosoma). The legs are attached to the cephalothorax, which contains the stomach and brain. The top of the cephalothorax is covered by a protective structure, the carapace, while the underside is covered by a structure called the sternum, which has…
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…divided into two parts, the cephalothorax (prosoma) and the abdomen (opisthosoma). The legs are attached to the cephalothorax, which contains the stomach and brain. The top of the cephalothorax is covered by a protective structure, the carapace, while the underside is covered by a structure called the sternum, which has…
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