Review: Depth, navigation and orientation in crabs: Angular acceleration, gravity and hydrostatic pressure sensing during path integration

This review shows how well the published work on the neural basis of balance and hydrostatic pressure reception in crabs agrees with the analyses and models of path integration. Fiddler crabs allow analyses at the level of behaviour. With considerable accuracy, they continuously show the direction to home with their body orientation and use idiothetic path integration to calculate a home vector from the internal measurements of their locomotion. All crabs have a well-developed vestibular system in the statocyst with horizontal and vertical canals which is used for angular acceleration sensing and depth reception. Large identified interneurones abstract the component of angular acceleration in one of the three orthogonal planes. These have properties consistent with a key role in path integration, combining vestibular and proprioceptor information with a central excitatory drive from the hemiellipsoid bodies. They have been monitored during walking, swimming and even in freefall for a 22 s period in parabolic flight.