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Final Submission
Cupra, the Bronze Larva Pokémon.
Black: It is born without a shell, and as such goes into hiding until fully developed. They are very rare in the wild.
White: This Pokémon can be found underground burrowing for elements. Its complex metabolism breaks nutrients into copper.
Black 2/White 2: Industrialization by humans has caused a lack of copper where this creature burrows, causing its shell to become weaker with time.

Argalis, the Silver Cocoon Pokémon.
Black: Ancient people revered Argalis as a deity due to the usefulness of its shell in technology. It sheds the pure silver shell from time to time.
White: This Pokémon's shell is often sought after by jewelers. It sheds its shell, which helps to cut down on poaching.
Black 2/White 2: Its shining shell is not seen until after evolution. No one knows whether the shell is formed during evolution, or if it actually causes evolution.