What is (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 called?

theca — (Zoöl.) (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. (Webster's 1913.)

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