Old Bluelip is supposedly a giant, deadly, blue-lipped clam. He only appears in the episode "Clams," in which he is the main antagonist.
Old Bluelip looks similar to all of the other clams in the series. He is a giant, light purple clam with blue lips and a large, pink tongue.
SpongeBob, Squidward, and Mr. Krabs are fishing for clams. SpongeBob accidentally rips Mr. Krabs' Millionth Dollar off of Mr. Krabs' pants and throws it in the water. Old Bluelip then tries to swallow the dollar, but SpongeBob manages to reel it in. However, he jumped up and took the dollar out of Mr. Krabs' hand.
He appears again at the end of the episode when Mr. Krabs jumps in his mouth to get the dollar. However, Old Bluelip takes Mr. Krabs, SpongeBob, and Squidward thought that he got eaten, but it actually turns out that only the lower part of Mr. Krabs' body got eaten so he could get the dollar back.
This character, along with the whole episode, is a reference to the Great White Sharks in the Jaws franchise.