Theca \The"ca\, n.; pl. {Thecae}. [L., fr. Gr. ? a case to put
anything in. See {Tick} a cover.]
1. A sheath; a case; as, the theca, or cell, of an anther;
the theca, or spore case, of a fungus; the theca of the
spinal cord.
[1913 Webster]
2. (Zool.)
(a) The chitinous cup which protects the hydranths of
certain hydroids.
(b) The more or less cuplike calicle of a coral.
(c) The wall forming a calicle of a coral.
[1913 Webster]