pearl oyster

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

• noun Any of several marine bivalve mollusks of the family Pteriidae and especially of the genus Pinctada that produce commercially harvested pearls.

from The Century Dictionary.

• noun A pearl-bearing bivalve mollusk of the family Aviculidæ, as Meleagrina margaritifera of Indian seas, and other species. See cut under Meleagrina.

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

• noun Any of several bivalve molluscs that are a source of pearls, but especially Pinctada margaritifera

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

• noun tropical marine bivalve found chiefly off eastern Asia and Pacific coast of North America and Central America; a major source of pearls