Shelley is SpongeBob's pet scallop. She lives in a birdcage that hangs from the ceiling of SpongeBob's bedroom. She first appears in the pilot episode "Help Wanted" and makes many appearances throughout the series.
Shelley is a small, lavender-colored scallop with a dark purple outline. She normally rests on a brown perch in a black birdcage hanging from the SpongeBob's bedroom ceiling. In some episodes, she is white with a blue outline and her perch is an orange-yellow color. In nighttime scenes, her color palette is a darker purple and her cage has a dark blue hue.
Shelley frequently appears in SpongeBob's room, but she has never been addressed directly in an episode. Her name is revealed in "The Bikini Bottom's Up Tour," a special feature on Disc 3 of The Complete 1st Season DVD. When the viewer selects her cage, Patchy talks about her and says that her name is Shelley. He explains that she does not do much but is a great pet.
Shelley and her cage are both normally part of the background, but they have been animated or moved on several occasions. In "Help Wanted," Shelley's cage moves back and forth when SpongeBob's alarm clock goes off. In "New Digs," SpongeBob puts Shelley in Mr. Krabs' office when he moves into the Krusty Krab. In "Don't Look Now," SpongeBob and Patrick put Shelley on SpongeBob's bed. In "Unreal Estate," SpongeBob gets stuck in Shelley's cage after sneezing.
SpongeBob's living room has a framed photo of Shelley on one wall and a photo of Gary on the opposite wall. This can be seen in "Banned in Bikini Bottom" and the online games Spring Cleaning and Bikini Bottom Mysteries Search.
So far, "Help Wanted" and "Unreal Estate" are the only episodes in which Shelley and her cage are animated apart from the background.