Where are the rainbow shells?

There are 50 of them in this game. I missed some of them.

Rainbow shells can be commonly found on the beaches of the water planet( once it's unfrozen), but also certain enemies drop them, and using the slippy oil item increases your chance at enemies dropping the said shells. Collecting fifty shells will get you the accessory called a Pooka string from the otter south of the dwarves home, and equipping it increases your mp recovery rate in battle.