On every move, the state of a Seashell changes: it can be open or closed.
A closed Seashell cannot be destroyed.
To hit an open Seashell, you must destroy a piece next to it by making a match, using a tool or a bonus. An explosion or a tool will also destroy the Seashell if it affects a cell with a Seashell. An opened Seashell can be empty, or contain a pearl which you need to complete the level.
You cannot move a Seashell.