What is the combination of the head and thorax called in a spider?

The combination of the head and thorax in a spider is known as the cephalothorax. This anatomical structure is a key characteristic of arachnids, which include not only spiders but also scorpions, ticks, and mites.

The cephalothorax serves as the central part of a spider's body, where the eyes, mouthparts, and legs are attached. Unlike insects, which have three distinct body segments (head, thorax, and abdomen), spiders have evolved to merge the head and thorax into this single, functional unit. This merging is significant as it reflects their adaptation and evolutionary path, providing a more streamlined body structure for their predatory lifestyle.

The other terms do not accurately define this specific body configuration in spiders. The abdomen is a separate section located behind the cephalothorax and contains vital organs but does not include the head or thorax. The thorax is generally a term used in the context of insects, while cephalum is not a recognized term in entomology or arachnology.