noun (n)

• a case or sheath especially a pollen sac or moss capsule(noun.plant)

  Synonym:
  sac
  

  source: wordnet30
• outer sheath of the pupa of certain insects(noun.animal)

  source: wordnet30
• 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.(noun)

  source: webster1913