pearl oyster

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of several bivalve marine mollusks of the genus Pinctada and related genera of tropical waters, especially P. margaritifera, a major commercial source of pearls.

Century Dictionary and Cyclopedia

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

Wiktionary

1. n. Any of several bivalve molluscs that are a source of pearls, but especially Pinctada margaritifera

GNU Webster's 1913

1. n. (Zoöl.) See under Pearl.
2. n. (Zoöl.) any one of several species of large tropical marine bivalve mollusks of the genus Meleagrina, or Margaritifera, found in the East Indies (especially at Ceylon), in the Persian Gulf, on the coast of Australia, and on the Pacific coast of America. Called also pearl shell, and pearl mussel.

WordNet 3.0

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