They are simply a group of skeletons that rest in graves and guard Floater's Cemetery. Their only variating features are their heads, with the rest of their skeletons being very similar.
Role in episode
When Mr. Krabs attempts to steal a valuable number one soda drinking hat from the grave of Smitty Werben Man Jansen, the skeleton comes to life and summons the rest of the army to protect the hat. Mr. Krabs fights the army successfully and runs off with the hat.