Often referred to as a univalve, a gastropod can be any of several mollusks with a single (univalve) shell and single muscle. Among the more common gastropods are the abalone, limpet, periwinkle, snail and whelk. With a few exceptions (such as the abalone), gastropods are not as highly regarded culinarily as bivalve mollusks such as the clam and oyster.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.