Noun
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.
The chitinous cup which protects the hydranths of certain hydroids.
The more or less cuplike calicle of a coral.
The wall forming a calicle of a coral.
Source: Webster's dictionaryThe filaments are fused to the corolla, while the anthers are generally connate (syngenesious anthers), thus forming a sort of tube around the style (theca). Source: Internet
The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore. Source: Internet