Metamorphosis

Metamorphosis is the transition in overall body pattern that occurs during the life history of some animals following birth or hatching. Two well-known examples are the development of caterpillars into butterflies and tadpoles into frogs.

Metamorphosis is considered an indirect form of development, in that a metamorphic animal passes through morphologically distinct stages before reaching the adult form. In contrast, humans and many other animals undergo direct development, in that the young and old resemble one another, except in size and sexual maturity. Metamorphosis occurs in at least 17 phyla of the animal kingdom, including Porifera (sponges), Cnidaria (jellyfish and others), Platyhelminthes (flat worms), Mollusca (mollusks), Annelida (segmented worms), Arthropoda (insects and others), Echinodermata (sea urchins and others), and Chordata (vertebrates and others). Although the term "metamorphosis" is generally not applied to plants, many plants have a developmental life cycle, called the alternation of generations, which is also characterized by a dramatic change in overall body pattern.