Final answer:
The immature form of an organism that looks different from the adult is called a larva, which eventually undergoes metamorphosis to become the adult form.
Step-by-step explanation:
The immature form of an organism that looks very different from the adult is called a larva.
Larvae usually have chewing mouthparts even if adult mouthparts are sucking ones, and at the last larval stage of development, the insect forms into a pupa. The pupa does not eat or move. Eventually, the pupa will metamorphose into the adult form of the organism.