Some vertebrates can go through nymph and pupa forms?

That statement is incorrect.

Nymph and pupa stages are characteristic of insects, which are invertebrates.

Vertebrates, which include mammals, birds, reptiles, amphibians, and fish, do not undergo metamorphosis with nymph and pupa stages.

Some vertebrates, like amphibians, do undergo metamorphosis, but it involves distinct larval stages (like tadpoles) that transform directly into adults, without nymph or pupa stages.