According the biogenetic law proposed by Haeckel, ontogeny recapitulates phylogeny. This in other words means that, the successive stages of individual development correspond with successive ancestors in the line of evolutionary descent. Nauplius larva occurs in the development of all the crustaceans and so it was considered as the ancestral form of crustaceans. The old idea of recapitulations stands greatly modified now-a-days and the crustacean larval forms are now regarded to be the larval reversions of simpler crustacean ancestors.
The larval forms are useful for finding out homologies and the affinities among various groups. The animals which pass through similar stages are closely related. Larvae are helpful in wide range distribution of species and also in keeping the food reserves of eggs to a minimum.