What is a sac containing small, calcareous concretions (otoliths). They are found in many Medusæ, and other invertebrates, and are supposed to be auditory organs called?

lithocyst — A sac containing small, calcareous concretions (otoliths). They are found in many Medusæ, and other invertebrates, and are supposed to be auditory organs. (Webster's 1913.)

Sources