Crabs have a split nervous system that consists of a dorsal ganglion, which is the crab's brain, and a ventral ganglion. A circumesophageal ganglion connects the two parts. The crab's brain is situated between its eyes, while the ventral ganglion is underneath its organs and between its legs.
A crab's brain is extremely small, even smaller than the point of a pencil. It processes information the crab collects with its eyes, while the ventral ganglion supplies nerves to the legs and sensory organs. One concern regarding a crab's brain is whether it is sophisticated enough to allow a crab to feel pain. While many studies conclude that the crab's brain is too small, some scientists do not agree.