Bikini Bottom's populace, like that of the rest of the series, consists of various anthropomorphic fish, whales, crabs, sponges, octopi, starfish, anchovies, lobsters, sharks, and most other forms of sea life, including sea monsters. Some forms of sea life, like jellyfish, seahorses, snails, and worms aren't sentient however, and are treated like pets or wild animals. An example of this is SpongeBob's pet snail, Gary. The first known land creature to live in Bikini Bottom was the Dark Knight, an ancestor of Sandy Cheeks, before the 12th century (Bikini Bottom was then known as Bikini Bottomshire).^[1] Sandy Cheeks, a squirrel from Texas, is (along with Jerry the Snail and Wormy the Butterfly) the only land creature seen living in modern Bikini Bottom.

"Animals" in Bikini Bottom are similar to those "animals" in the real world. Some are treated as pets, while others live in the wild.

A majority of "animals" live in the wild. First and foremost, jellyfish are similar to bees. There are many types of jellyfish that live in Bikini Bottom. Pink are the most common, blue are uncommon, green are rare, purple are very rare and only one albino jellyfish exists. White and orange jellyfish are seen in the videogame Lights, Camera, PANTS!. Jellyfish reside mainly in Jellyfish Fields, which has a population of four million jellyfish. They make and live in hives, another similarity to real-world bees. In earlier episodes, jellyfish were plain pink, but later on, more jellyfish began to appear with spots, but plain pink ones still exist. Jellyfish are similar to cows in that they can be "milked" for their fresh jellyfish jelly. Second, scallops are similar to birds. They are usually found in groups at Goo Lagoon, particularly acting as seagulls. Scallops are usually orange or purple. There is also a colossal clam named Clamu in the Bikini Bottom Stadium. It's currently a mother of one. Third, seaslugs were seen in the video game, SpongeBob SquarePants: SuperSponge. They are known to dislike everyone. Fourth, seahorses, which are similar to horses, can be ridden and are very interested in food. Fifth, the Alaskan Bull-Worm is a large, omnivorous worm that attacked various parts of Bikini Bottom in its sleep in "Sandy, SpongeBob, and the Worm". It eventually went on to destroy the entire city. Sixth, sea urchins, which are small "bug-like" creatures whose bites cause severe itchiness (a possible similarity to fire ants or mosquitoes). Seventh, Nematodes which are worm like creatures that travel in groups and consume common objects by eating or drinking them. They once destroyed SpongeBob's house by sucking the pineapple juice out of it.^[12]

Other "animals" are treated as pets. Two well-known "pets" are snails and worms. Snails are similar to cats and are common as pets, but they are also known to lurk in alleys and forests. A well-known character Gary the Snail is one of them. Worms are similar to dogs, and are also common as pets. At one point SpongeBob also owned a worm.