What are the two major body regions of arachnids?

• A. Head and thorax
• B. Cephalothorax and abdomen
• C. Thorax and abdomen
• D. Prosoma and opisthosoma

Answer: (B)

Arachnids are organized into two major body regions: the front region, which is a fused head and thorax called the cephalothorax, and the rear region, the abdomen. The cephalothorax bears the eyes, mouthparts, and legs, while the abdomen contains most of the internal organs and, in spiders, the spinnerets used for silk. Using cephalothorax and abdomen is the standard terminology you’ll see in many introductory texts and exams, making it the clearest and most widely accepted pairing for describing arachnid anatomy. Note that prosoma and opisthosoma refer to the same regions, but cephalothorax and abdomen is the conventional terms set used in many resources.