An arrangement of mechanoreceptors that detects the direction of gravity. Invertebrates typically have some kind of statocyst, a cavity that contains a statolith, the position of which in the cavity can be detected by mechanoreceptors in the wall of the cavity. In many marine animals the statolith is a grain of sand that is incorporated into the statocyst. If lobsters (Decapoda) are kept in an aquarium containing iron filings, then these get taken up into the statocysts. By using a magnet, it is possible to alter the apparent direction of gravity, and the lobsters change their orientation accordingly. In vertebrates a similar principle operates in the vestibular apparatus of the inner ear.
Subjects: Zoology and Animal Sciences.