Jellyfish are gelatinous, free-swimming creatures common throughout all oceans of the world. They can have any number of spots and appear in hives much like bees. They make jelly, in a similar manner to bees making honey.
In the series, jellyfish are featured very prominently. Jellyfish Fields, a major location in the SpongeBob SquarePants universe, is home to over 10 million jellyfish, as seen in Jellyfish Hunter. The hunting and catching of jellyfish, known as Jellyfishing, is a popular hobby among sea folk, most notably SpongeBob and Patrick . It is similar to butterfly catching and is typically done only for fun/sport, with the jellyfish being released unharmed. Jellyfish appear in almost all SpongeBob video games, typically as basic enemies or background add-ons. They are usually caught using Jellyfish Nets or jars. They sometimes spook the Bikini Bottomites, but never try to hurt them, unless in self-defense.
Jellyfish live in Jellyfish Fields; they allow themselves to be caught (jellyfishing) by SpongeBob and Patrick while other times they sting them, which is a running gag. They are in tune with nature and have great rhythm. They are a constant presence in Bikini Bottom. They also allow SpongeBob to squirt out Jellyfish Jelly, which is especially tasty. While most others dare not trespass in Jellyfish Fields, SpongeBob loves them all.
Jellyfish in SpongeBob SquarePants are portrayed in a stereotypically cartoonish manner, and are typically pink in color. In the same manner as snails are likened to cats and worms are likened to dogs, jellyfish display many qualities of bees. They produce edible jelly in the same manner bees produce honey, and their stings have similar effects to those of bees, often causing swollen bumps (in real life, a jellyfish's sting can range from mild to life threatening). They also make a buzzing sound just like bees, are very small compared to main characters. Since Bikini Bottomites are stated to be only smaller than a human’s foot shown in The SpongeBob SquarePants Movie, this would make jellyfish almost microscopic.
Pink Jellyfish - The most common jellyfish. Usually has 3 or 8 spots depending on its size.
Blue Jellyfish - a very rare kind of jellyfish. In "Revenge of the Flying Dutchman", a blue jellyfish moves in a circle. In "Battle for Bikini Bottom", they have 2 health points rather than 1. On the show, one appears in the episode Jellyfish Hunter and is called "No-Name" by SpongeBob until the end, where it is renamed "Friend". It also told SpongeBob to "bring it on" earlier in the episode, marking the first time a jellyfish has spoken.
No name/Friend - A mysterious blue jellyfish that appears in "Jellyfish Hunter". Named so because he was the only jellyfish in Jellyfish Fields who SpongeBob has never been able to catch and give a name to. He later helps SpongeBob stop Mr. Krabs, and is renamed "Friend".
Big Lenny - An enormous and dangerous jellyfish whose stings are almost always fatal. The only person known to have survived one is named Doctor Manowar, who has a gigantic swelling on the side of his head as a result. This swelling only hurts when someone touches it. Big Lenny could be a Man O War or a box jellyfish as their stings are known to kill people. Big Lenny is seen in "I'm Your Biggest Fanatic" as a picture and in the PC game "Operation Krabby Patty" during the jellyfishing game.
Jamming Jellyfish- A jellyfish that SpongeBob brings home as a pet in "Jellyfish Jam". SpongeBob and the jellyfish have a disco party. It then invites hundreds of other jellyfish to SpongeBob's house, which they invade and throw a massive dance party in.