Why is the aplysia such a popular animal for single-cell studies of learning?

Aplysia is a marine gastropod mollusc which is an often used model organism in neuroscience, especially on the cellular biology of learning and memory. What makes them easy to work with are their giant neurons, which are one of the largest. Aplysia neurons are suitable for studies of how neurons and neural circuits control behaviours. Its defensive reflex has been studied because it is mediated by electrical synapses, which allow several neurons to fire synchronously.