statocyst

noun

1. 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).

   “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.”