Which of the following animals does not undergo metamorphosis?

All the given animals except earthworm undergo metamorphosis. Earthworm exhibits direct development where no larval stage is involved.
Metamorphosis is usually seen in animals exhibiting indirect development, involving a larval stage which Later transformed into an adult.
The larval form of moth is a caterpillar and that of tunicates is a tadpole.
In starfish, bipinnaria larva forms into adult.