‖n.; pl. L. Hydrothecæ E. Hydrothecas [ NL., fr. E. hydra + Gr. &unr_; a box. ] (Zool.) One of the calicles which, in some Hydroidea (Thecaphora), protect the hydrants. See Illust. of Hydroidea, and Campanularian. [ 1913 Webster ]