Snails like other invertebrates do not have a spinal cord nor one single brain. Instead they have a set of ganglia (groupings of neurons) that distribute the control of the various parts of the snail.
In Pulmonates, the ganglia are arranged in a circle around the digestive system. The number and arrangement of ganglia are variable but will have:
- 2 cerebral ganglia supplying the eyes, tentacles and head
- 2 pedal ganglia supplying the foot muscles
- 2 pleural ganglia supplying the mantle cavity
Other ganglia supply the buccal cavity which serves the radula [teeth]. The parietal ganglia supply the lungs. Lastly, the visceral ganglia supply the remaining organs of the visceral cavity. There is no optic ganglion (Kerut & Walker 1975).
These very small cerebral ganglia contain 4000-100000 individual cells often called neurons. The pattern of nerves varies from species to species.
Although this is a rudimentary brain, snails and slugs have more ability for associative thinking than most people give them credit for.
Nobel Prize scientist, Eric Kandel, an American neuropsychiatrist who studied how memory works and how memory is stored in neurons, used a Mollusc similar to a snail, a sea slug [we call them sea hares] Aplysia californica, to study how neurons worked. He used it because he decided that this was the simplest group of animals known to be capable of learning.