Word Study
hydrotheca
CIDE DICTIONARY
hydrotheca, n. [NL., fr. E. hydra + Gr. a box.].
One of the calicles which, in some Hydroidea (Thecaphora), protect the hydrants. See Illust. of Hydroidea, and Campanularian. [1913 Webster]
For further exploring for "hydrotheca" in Webster Dictionary Online