Don Knotts' bespectacled Mr. Limpet makes an under the sea cameo in The Little Mermaid. Although The Incredible Mr. Limpet (1964) was a combination live-action/animated film produced by Warner Bros., Knotts appeared in numerous Disney films, including The Apple Dumpling Gang (1975), Herbie Goes to Monte Carlo (1977) and Chicken Little (2005).
Image © Walt Disney Animation