A shell is a large clam shell. In Kirby Mass Attack, its exterior is purple and its interior is red and sparkly. The front is adorned with a yellow star design. In Kirby and the Rainbow Curse, shells are bit more plain. They have pink exteriors and gray interiors.
Shells appear in underwater stages, primarily in Green Grounds and Dedede Resort. When a Kirby strikes a shell, it opens. Some shells contain nothing, while others hold air bubbles, medals, and even optional doors. Some shells are actually Shellmics in disguise, something the player should bear in mind before opening one.
There are large, orange shells in the game as well. These are rare and take numerous consecutive hits to open. They always contain Treasure Chests.