They look exactly like normal peanuts. They come in a red and white-striped bag that reads the food's name in mint-green text, with the stripes outlined by dark blue.
Role in episode
SpongeBob and Patrick visit the Oyster Stadium to see Clamu the giant oyster perform tricks, only for her to be sleeping. SpongeBob throws a Sea Peanut at Clamu to wake her up, causing her to stir.
After Patrick is given no choice but to agree that he is the culprit of the incident rather than his best friend, he is taken to the Oyster Stadium, where he is chained to a platform in the middle of the stage and pelted with Sea Peanuts by the angry audience for the crime.
However, at the end, it is revealed that the person who caused Clamu distress is Mr. Krabs, who stole her egg, believing it to be a pearl, to take for free on The Bikini Bottom Annual Free Day. As a result, the audience throws Sea Peanuts at Mr. Krabs instead.