The Collaborative International Dictionary
Tentaculocyst
Tentaculocyst \Ten*tac"u*lo*cyst\, n. [Tentaculum + cyst.] (Zo["o]l.) One of the auditory organs of certain medus[ae]; -- called also auditory tentacle.
Wiktionary
tentaculocyst
n. (context zoology English) One of the auditory organs of certain medusae.