statocyst

A small organ of balance in many invertebrates, consisting of a fluid-filled sac containing statoliths that stimulate sensory cells and help indicate position when the animal moves.

An organ in certain animals, such as crustaceans and jellyfishes, which enables its owner to orient itself in a definite position with respect to gravity.

A balance organ present in some aquatic invertebrates, consisting of a sac-like structure containing a statolith and numerous innervated setae.