In general, among Mollusks, the mouth opens into a buccal cavity. In most classes of Mollusks, the buccal cavity contains a tongue called the odontophore. The odontophore possess multiple rows of teeth called radula that chitonous and flexible. Among Mollusks the number of teeth can range from a few to over 100,000. The size, number, and arrangement of the radula also vary considerably and often used as diagnostic tool for distinguishing species. In some gastropods the radula is used in a rasping or conveyor belt fashion and be used to drill holes through hard parts of other organisms. The image above from here is from the whelk Busycon carica (Gmelin, 1791). Below is an Apple Snail in rasping material of the side of aquarium.
Below the fold is another way gastropods feed.
Feeding in Holothurians not so cool. Most are suspension or deposit feeders. Some species extend there nasty branched, mucus-covered tentacles into the water to trap particles. Those nasty mucus and dirt covered tentacles are then put into the mouth. Other species plow through the mud using their tentacles to selectively feed on particles. Apparently, they are also picky eaters.