perigonium

Etymology
From.

Noun

 * 1)  The sterile parts of a flower; collectively, the sepals and petals (or tepals); the perianth.
 * 2)  The modified leaves around the antheridia in a bryophytic plant.
 * 3)  The wall of the sporosac in a hydroid.
 * 1)  The wall of the sporosac in a hydroid.