The complete larval development of Romaleon gibbosulum, comparing five zoeal stages and one megalopal stage, and the first zoea of Metacarcinus magister are described and illustrated. The zoeal morphologies of the two species are compared with those known for other Cancridae species. Based on the zoeal mouthparts, R. gibbosulum shows more affinity to species of Glebocarcinus than its congeners. Metacarcinus magister is different from its congeners and coincides well with Cancer productus. These results may indicate that a re-examination of their generic classification is necessary.