The Appetizer is a monster made by Mr. Krabs that was originally supposed to be a type of food. It is unknown how it turned into monster. It only appeared in the episode, Squilliam Returns. It tried to eat Mr. Krabs and Patrick.
The Appetizer is a giant pile of brown food goop and sludge with sharp teeth and one eye. Items that can be seen on it is a foot, a purple shell, a palm tree, bug wings, bug legs, and seaweed. It may have 6 teeth but that doesn't mean there is not more.