Tropical and subtropical waters. They usually live on mud bottoms in colonies that may number millions of individuals. Their shells are often eroded and need much cleaning. Almost all species remain cheap because the collector can pick up the gems and fairly clean indivuals when field collecting. A few live in deep water and are hard to obtain. The little interest they obtain from most collectors must be due to a lack of knowledge on the group that contains some magnificent shells such as Pseudovertagus nobilis and Rhinoclavis. About 400 species.