Adult barnacles are sessile, but the larvae are free-swimming. A second example of the adaptive significance of metamorphosis is in barnacles (Arthropoda phylum). Thus, adults and larvae do not compete for food, a limiting resource in many environments. For example, adult amphibians (Chordata phylum) often eat very different foods than their larvae. Metamorphosis is associated with adaptive changes in the way an organism interacts with its environment, and this may be why it evolved independently in so many different phyla of the animal Such a model provides a framework for studies of metamorphosis, although there is clearly much more to metamorphosis than implied by this simple model. Thus, in the case of a butterfly, a very simple model of metamorphosis is that one family of genes is expressed in the larva (caterpillar), a second family of genes in the pupa, and a third family of genes in the imago (adult). At the molecular level, highly regulated temporal and spatial changes in gene expression causes metamorphosis in all animals. In general, cells in the different parts of a multicellular organism all have the same genes, although only some of these genes are expressed (translated into proteins) in any given cell. 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. 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). 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 is considered an indirect form of development, in that a metamorphic animal passes through morphologically distinct stages before reaching the adult form.
![stages of metamorphosis stages of metamorphosis](https://i.pinimg.com/originals/9d/a7/cf/9da7cfe9fb6098a09f9f0205b47deee8.gif)
Two well known examples are the development of caterpillars into butterflies and tadpoles into frogs.
![stages of metamorphosis stages of metamorphosis](https://s3.amazonaws.com/libapps/accounts/83995/images/stagesofchange.jpg)
Metamorphosis is the transition in overall body pattern that occurs during the life history of some animals following birth or hatching.