Aplysia gill and siphon withdrawal reflex

The Aplysia gill and siphon withdrawal reflex (GSWR) is an involuntary, defensive reflex of the sea hare Aplysia californica, a large shell-less sea snail or sea slug. This reflex causes the sea hare's delicate siphon and gill to be retracted when the animal is disturbed. Aplysia californica is used in neuroscience research for studies of the cellular basis of behavior including: habituation, dishabituation, and sensitization, because of the simplicity and relatively large size of the underlying neural circuitry.

Eric Kandel, recipient of the Nobel Prize in Physiology or Medicine in 2000 for his work with Aplysia californica, was involved in pioneering research into this reflex in the 1960s and 1970s.