Mission Shells are shells scattered throughout the map. Upon the discovery of a shell, a mission will be unlocked, making it available for completion and revealing what you must do to complete the mission. Missions are tasks which are assigned to all sharks in Hungry Shark Evolution except for the Top Secret Lab Sharks. These missions give rewards of coins when completed when unlocked.
A Super Mission is unlocked for each shark when all previous missions have been completed. The Super Mission yields the greatest reward of all missions for that shark, generally more than triple the amount. Every super mission requires you to achieve a certain amount of points in one run.
The bigger/later obtained the shark, the harder the missions.