Esmerelda is a snail who appears in the episode "Sanctuary!" She is mistaken for a male by SpongeBob and nicknamed "Señor Poopus."
She is similar in appearance to Gary. However, she has a light olive green body with a mustard yellow underside, a light purple shell with ten blue spots, a red-orange spiral, and thick light brown eyebrows. She appears to be a stray snail in bad shape, as indicated by her withered eyestalks, visible ribs, and a large deforming dent in her shell.
In "Sanctuary!," SpongeBob and Gary come across Esmerelda hiding behind a rock. Shy at first, she is quickly adopted by SpongeBob, who takes her home, names and feeds her. She appears to be friends with Gary. In the end of the episode, Bob Barnacle comes to SpongeBob's house and takes her to his shelter. He also tells SpongeBob that her name is Esmerelda and not "Señor Poopus."
She is the second pet SpongeBob has owned that he initially thinks is a male, but is later revealed to be a female, the first being Mrs. Wormsley from “Pet or Pests.”