Mussels are molluscs and are related to water snails. Because their shells are divided into two halves, they are called bivaldes. The shell protects the soft body of the animal. A powerful foot enables the animal to
change its position. Mussels suck in water and extract the oxygen and food that they require. There are both marine and fresh water mussels and can be found worldwide. The marine mussels prefer cool seas.Freshwater mussels, also known as naiads, inhabit streams, lakes and ponds and there are around 1,000 known species. The shells are dark blue or dark greenish brown on the outside, while on the inside they have a pearly appearance. Mussels attach themselves to solid objects or to one another by strands called byssus threads and often appear in dense clusters.