Flexi Says: Most mollusk have two organs that are unique to this phylum: a specialized feeding organ called a radula and a dorsal layer of tissue called a mantle. The mantle is a soft tissue layer that is formed from folds of the dorsal body wall. It lies beneath the shell where it covers the body of the animal. The mantle has several critical functions. The outer cells of the mantle secrete layers of calcium carbonate that form the shell. A second important role of the mantle is in the formation of a cavity called the mantle cavity. The mantle cavity is formed between the mantle tissue and the body of the animal. This cavity serves as a water pumping station for aquatic mollusks. The radula is a specialized muscular feeding organ that contains teeth made of a carbohydrate (chitin) substance. It is located in front of the mouth in the head region of all mollusk classes except Bivalvia. This makes sense since bivalves are filter feeders that lack a distinct head region. Some mollusks use the radula to scrape food, such as algae, off of rocks and into the mouth, while other predatory species use it to drill holes into the shells of their prey.
