peristome

noun3

1. •
   One or two rings of tooth-like appendages surrounding the opening of the capsule of many mosses.

   • Its removal does not, however, leave the mouth of the capsule wide open, for around the margin are two circles of pointed teeth forming the peristome. — 1911
2. •
   The parts of or surrounding the mouths of numerous invertebrates.
3. •
   The lip, or edge of the aperture, of a spiral shell.