[Free Registration/Login may be required to access all resource tools.] Crustaceans are a large group of arthropods, consisting of almost 52,000 species. The majority of crustaceans are aquatic. A few groups have adapted to living on land. Crustaceans are among the most successful animals and are found as much in the oceans as insects are on land. Learn more about crustaceans in this learning module produced by CK-12.