From Muppet Wiki

Toto is the traditional canine companion of Dorothy Gale in The Wizard of Oz. In The Muppets' Wizard of Oz, however, Toto is a king prawn, rescued from Aunt Em's Diner. Aunt Em objects to dogs, because they smell funny and mess up the carpet. Toto is one of Dorothy's few friends in Kansas, and she rushes back into the trailer to rescue the crustacean.

Once transported to Oz, however, Toto, having broken out of his tank has enlarged, is nude, and speaks with a Spanish accent. Dorothy supplies Toto with costuming, and the prawn in return tries to become Dorothy's agent.

Other Portrayals

Foo-Foo took on a more traditional portrayal of the role in The Muppets Go to the Movies.