statocyst

1. (zoology) An organ of balance found in some aquatic invertebrates, consisting of a sac-like structure containing a statolith and numerous innervated setae. Ancestral to vertebrate otolith (their organ of hearing and balance).Examples: "Despite their tiny size, statocysts encode significant information about an animal's buoyancy and swimming ability, as we know from studying statocyst variability among modern cephalopods."