Theca > define

• (n.) 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.
• (n.) The more or less cuplike calicle of a coral.
• (n.) The wall forming a calicle of a coral.
• (n.) The chitinous cup which protects the hydranths of certain hydroids.

noun

• A case or sheath especially a pollen sac or moss capsule.
  • synonyms: sac
• Outer sheath of the pupa of certain insects. .