filter feeder

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

• noun Any of various aquatic animals, such as clams, sponges, and certain whales, that feed by filtering small organisms or organic particles from water.

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

• noun biology Any aquatic animal that obtains nourishment by filtering particles of food from the water in which it lives