Radula is present in animals belonging to phylum-Mollusca. It is a rasping organ of molluscs situated in a sac on the underside of buccal cavity.
It is used for tearing plant material by rubbing it against the hardened surface of the mouth. Suckers are present in parasitic platyhelminthes to enable them to absorb nutrients from the host.
Undulating membrane and sucktorial organs are present in ciliated protozoans. Ctenidia are the gills of aquatic molluscs.