Filter Feeders

Some animals feed on plankton floating in the aquatic environment. To trap this rich source of food, water is drawn towards the animal either by

• The movements of its appendages; or

• The action of cilia.

The water usually passes through a kind of sieve at the front end of the gut which filters out the food before the water passes out of the body. Large amounts of water are continuously drawn in through the filtering device in this way. Some examples of filter feeders are whales, flamingoes, oysters, mosquito larvae and copepods.

   Certain whales have baleen instead of teeth on their upper jaws. The baleen consists of closely packed plates of whales bone which acts as a strainer. It separates out the plankton from the water which enters the whale mouth. The flamingo has a straining device in its bill to separate out food particles in muddy waters.

    Oysters , gills are used to strain food. The action of the cilia on the gills draws in water. The food in water is trapped by the mucus covered surface of the gills. This food is then pushed towards the mouth by the action of the cilia. The mosquito larva has a pair of mouth parts, each bearing a dense fringe of bristles. These are called feeding brushes. The continuous revolving movements of these brushes sweep water containing microscopic organisms into the food particles in the foregut.

    In planktonic copepods, water currents are caused by special brush like appendages which vibrate between 600 and 2640 times a minute. The water is directed into a filter chamber where the tiny food particles are filtered out.