墨西哥钝口螈（学名：Ambystoma mexicanum，英文：Axolotl），又名「美西螈」，俗称「六角恐龙」，是水栖型的两栖类，是墨西哥的特有种，因其独特的外貌及幼态延续而著名。也就是说，即使在性成熟后也不会经历适应陆地的变态，仍保持牠的水栖幼体型态。墨西哥钝口螈的「不老容颜」使得牠成为许多科学家研究的对象。虽然在全球有作为宠物而被饲养（特别是北美等地），但其原栖地已被大量开发，可生活面积不多于10平方公里。目前原生种在IUCN红色名录内被评为极危物种。

The axolotl (/ˈæksəlɒtəl/, from Classical Nahuatl:āxōlōtl [aː.ˈʃóː.loːtɬ]) also known as a Mexican salamander (Ambystoma mexicanum) or a Mexican walking fish, is a neotenic salamander, closely related to the tiger salamander. Although the axolotl is colloquially known as a "walking fish", it is not a fish, but an amphibian. The species originates from numerous lakes, such as Lake Xochimilco underlying Mexico City. Axolotls are unusual among amphibians in that they reach adulthood without undergoing metamorphosis. Instead of developing lungs and taking to land, the adults remain aquatic and gilled.