Shellder (Japanese: シェルダー Shellder) is a Water-type Pokémon introduced in Generation I. It evolves into Cloyster when exposed to a Water Stone.

What Gen is Cloyster?

Cloyster (Japanese: パルシェン Parshen) is a dual-type Water/Ice Pokémon introduced in Generation I. It evolves from Shellder when exposed to a Water Stone.

Where can I find Shellder Gen 1?

Locations: You can catch Shellder in various locations in the game by using a fishing rod. Look for it on Routes 6, 11, 19, 20 and 21, as well as Vermilion City in Red/Blue. It's more rare in Pokemon Yellow, but you should still be able to find it on Routes 17 and 18 without a problem.