Classes Caudofoveata and SolenogastresThese two small classes are often combined by other authors to form the class Aplacophora. Both classes contain relatively few species. The Caudofoveata are aberrant molluscs which lack shells. They normally burrow in soft sediments and are quite common in the deep sea. The class Solenogastres is also very small. These animals also lack shells and generally live epibenthically i.e. on the surface of the substratum.