The class of invertebrates in which the young one looks completely different from the adult form is known as holometabolous organisms.
In holometabolous organisms, the young one known as the larva is completely different from the adult and the process in which the larva transforms into an adult is known as metamorphosis.
For the process of metamorphosis, the following life stages occur,
Adult ---> egg---->larva--->pupa ---> adult
E.g is a butterfly in which the larva (caterpillar) looks completely different from the adult butterfly.
