Malacology is the study of mollusks. This includes animals like octopus, snails, slugs, and clams. It is the second largest phylum of animals, making them one of the most successful groups on the planet. There are over 80,000 described species of mollusks with many more left to be discovered. Mullusca is composed of 8 recognized classes including Cephalopoda, Gastropoda, Polyplacophora, Scaphapoda, Monoplacophorans, the Aplacophorans, Caudofoveata and Solenogastres, and Bivalvia.