Spot is a tiny translucent green amoeba, and is also just the right size for Plankton. He also has an antenna and three dark green spots on him, with four legs on each side of his body. He seems to act like a dog. He only has one eye and likes walking and barking.
Plankton once again attempts to steal the Krabby Patty recipe, but fails as usual. He agrees with Karen that he should find something to get his mind off of the formula. He decides to get a pet. He goes to the Animal Shelter with SpongeBob to find a pet. While browsing the pets, Plankton almost gets attacked by a moldy clam (that seemingly looks like algae on a rock). As the clam is about to devour Plankton, Spot comes in and barks at the clam and bites its tongue, which is holding Plankton, and saves him. Plankton and Spot grow on each other and Plankton decides to adopt him as his pet.
Plankton wanted him to be a guard dog, but due to Spot being nice, he decides to make him a retriever. He also has the ability to grow in size and scare off any enemies who try to harm Plankton.
Spot also has the ability to eat a Krabby Patty in one bite. After he got one, he came to the Chum Bucket with it. He was offered half of Plankton's laboratory, but after eating the Krabby Patty, he got disciplined.
Spot went missing, after Plankton became upset with him. He looked all over for Spot, with SpongeBob's help. Eventually, Plankton finds Spot on his eye because of the small size.
Spot is the third amoeba seen in the series. The first appearance were the Amoebas seen in "Patty Hype" where Mr. Krabs watches a show about them on television and the second appearance of Amoebas are the ones that were seen at the end of the episode, "Goo Goo Gas."