peristome

/P EH1 R AH0 S T OW0 M/
noun
  1. 1

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

  2. 2

    The parts of or surrounding the mouths of numerous invertebrates.

  3. 3

    The lip, or edge of the aperture, of a spiral shell.

Source: https://en.wiktionary.org/wiki/peristome