Functions of Cilia and Flagella

Cilia and flagella are involved in locomotion, feeding, cleansing, respiration, circulation and passage of materials.

1. Locomotion. Cilia or flagella re responsible for locomotion in cilinate and flagellate Protozoa, Ctenophores, some Platyhelminthes and Nemertea, rotifers, some snails and the ciliated larvae of Annelida, Mollusca and Echinodermata. In Paramecium the cilia cover the entire body surface, and the protozoan swims by the help of its cilia. In the larva of Annelida, Mollusca and Echinodermata cilia are arranged in bands. In the free-living flatworm Planaria the ventral surface of the body is covered by cilia. Beating of the cilia results in a slow glinding movements over the substratum.

2. Feeding. Many sessile or sluggish animals are ciliary filter feeders, e.g. the lancet Amphioxus, the ascidian Herdmania, rotifers, and the fresh water nussel. Ciliary currents bring in fine particle of food which are then trapped by the animal. In the sea anemone the tentacles are bent towards the mouth and the cilia sweep food materials into the body cavity. In some echinoderms and mollusks the cilia help in the transport of food in the digestive system.

3. Cleansing. In many sea anemones and corals, cilia on the tentacles and the oral region sweep unrequired particles away from the mouth and thus have a cleansing effect. The beating of cilia from the mouth the anus in many starfish also helps in sweeping debris.

4. Respiration. Water currents created by cilia facilitate respiration. The continuous movement of water helps exchange of gases.

5. Circulation. In animals lacking a true blood-vascular system, e.g. some annelids like Tomopteris, the coelomic fluid is kept circulating by ciliary tracts. In the starfishes, also, the coelomic fulid is circulated by ciliary action.

6. Passage of materials. The cilia lining the lumen of nephridia, kidney tubules, and genital ducts help in the passage of materials through these structures.