Earthworm does not undergo metamorphosis.
Starfish, moths and tunicates all undergo metamorphosis that is, they develop into the adult organisms after undergoing many developmental stages in their lives as young ones. Metamorphosis is usually seen in amphibians and insects. however, in earthworms, young ones that look like miniature versions of adults are born from the cocoons.

Answer:

The organism that does not undergo metamorphosis is the tunicate.

Metamorphosis

Metamorphosis is a biological process that involves a complete transformation in the body structure of an organism. It is a common phenomenon observed in many animals during their developmental stages. Metamorphosis helps the organism to adapt to different environments and life stages.

Earthworm

Earthworms are segmented worms that belong to the phylum Annelida. They undergo a type of metamorphosis called ecdysis, which involves shedding their outer layer of skin to grow. Earthworms do not undergo a complete metamorphosis.

Starfish

Starfish are marine animals that belong to the phylum Echinodermata. They undergo a type of metamorphosis called bipinnaria larval stage, which involves a transformation from a ciliated larva into a juvenile starfish. Starfish undergo an incomplete metamorphosis.

Moth

Moths are insects that belong to the order Lepidoptera. They undergo a complete metamorphosis, which involves four distinct stages: egg, larva (caterpillar), pupa (cocoon), and adult (moth). The pupal stage is the most dramatic stage of metamorphosis, during which the moth undergoes a complete transformation from a worm-like caterpillar to a winged adult moth.

Tunicate

Tunicates are marine animals that belong to the phylum Chordata. They undergo a type of metamorphosis called retrogressive metamorphosis, which involves a transformation from a free-swimming larva into a sessile adult tunicate. Unlike other animals that undergo metamorphosis, tunicates do not undergo a complete transformation in body structure.

Conclusion

In conclusion, the tunicate is the organism that does not undergo metamorphosis. While other animals like earthworms, starfish, and moths undergo metamorphosis, the tunicate undergoes a unique form of metamorphosis that involves a retrogressive transformation from a free-swimming larva to a sessile adult.