||Hy`dro*the"ca (?), n.; pl. L. Hydrothecæ (#), E. Hydrothecas (#). [NL., fr. E. hydra + Gr. ? a box.] (Zoöl.) One of the calicles which, in some Hydroidea (Thecaphora), protect the hydrants. See Illust. of Hydroidea, and Campanularian.