The Collaborative International Dictionary
Lithocyst
Lithocyst \Lith"o*cyst\ (l[i^]th"[-o]*s[i^]st), n. [Litho- + cyst.] (Zo["o]l.) A sac containing small, calcareous concretions (otoliths). They are found in many Medus[ae], and other invertebrates, and are supposed to be auditory organs.
Wiktionary
lithocyst
n. (context zoology English) A sac containing otoliths, found in medusae and other invertebrates.