"Simple tentaculocyst of one of the Trachomedusae (Rhopalonema velatum). The process carrying the otolith or concretion hk, formed by endoderm cells, is enclosed by an upgrowth forming the "vesicle," which is not yet quite closed in at the top." — Encyclopedia Britannica, 1893

Trachomedusae

"Simple tentaculocyst of one of the Trachomedusae (Rhopalonema velatum). The process carrying the otolith…