An invertebrate, like a jellyfish, a clam, or a worm, does not have the genes necessary to construct a vertebrae, or all the other muscles, nerves, and organs needed by animals with a backbone, including fish.
A functioning fish does not possess the genes necessary to construct and utilize legs. Tadpoles, which live in the water and have no legs, change into land-dwelling frogs with legs.
Tadpoles are not fish. They may look like a guppy, but they are the offspring of fully functioning frogs, complete with all the genes for legs and the structures needed to use them. The tadpole is not yet fully grown, and in the incomplete stage has not acquired all the features present in the adult, but it is a juvenile frog.
However, it does have all the genes needed for life in the water, as well as those genes needed to grow legs at the right time, then live on land, and eventually produce tadpoles which themselves become frogs. No new genetic information must be acquired by mutation as required by evolution. They are already present.
This could be said about a human fetus in its early stages. At one point it has no arms or legs (or eyes or lungs etc.) but it acquires them through genetically controlled growth. No evolutionary process is needed to transform a fertilized human embryo into a baby and then into an adult. All the genes are present at the start.
Neither growth nor metamorphosis are evolution.
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