peristome

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Botany A fringe of toothlike appendages surrounding the mouth of a moss capsule.
• noun Zoology The area or parts around the mouth in certain invertebrates.

from The Century Dictionary.

• noun In botany, the ring or fringe of delicate hairlike appendages which is observed on the rim or mouth of the capsule of a moss when the operculum is removed.
• noun In zoology, mouth-parts in general; the structures or set of parts which surround the cavity of the mouth or oral opening and constitute its walls, framework, or skeleton: used chiefly of lower animals, as echinoderms, which have circular or radiate mouth-parts.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) The fringe of teeth around the orifice of the capsule of mosses. It consists of 4, 8, 16, 32, or 64 teeth, and may be either single or double.
• noun The lip, or edge of the aperture, of a spiral shell.
• noun The membrane surrounding the mouth of an invertebrate animal.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun botany One or two rings of tooth-like appendages surrounding the opening of the capsule of many mosses.
• noun zoology The parts of or surrounding the mouths of numerous invertebrates.
• noun The lip, or edge of the aperture, of a spiral shell.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (botany) fringe of toothlike appendages surrounding the mouth of a moss capsule
• noun region around the mouth in various invertebrates