Platyhelminthes, commonly referred to as flatworms, are divided into the Catenulida and Rhabditophora classes. There are over 29,000 discovered species of Platyhelminthes and it is likely that there are thousands more. Most Platyhelminthes flatworms are either flukes or tapeworms, both of which are parasitic. They have a bilateral body symmetry and are completely flat. Most live on land but non-parasitic flatworms live on the ocean floor.