Zoonule (/ˈzuːnjul/) is a term used to describe a small anatomical structure found in certain animals, such as crustaceans and insects. The word is derived from the Greek "zoion" meaning "animal" and "ule" meaning "small". The correct spelling of the word is Zoonule with a double "o" as opposed to Zoanule. While the latter spelling may be tempting due to the similarity to the word "zone", it is incorrect and should be avoided.