Any of several salamanders(genus Ambystoma) native to Mexico and the western United States that, unlike most amphibians, often retain their external gills and become sexually mature without undergoing metamorphosis.

• 美西蝾螈几种原产于墨西哥和美国西部地区的蝾螈（蝾螈属），不象大多数别的两栖动物，它们一般保留外部的腮且不用经历变形就成熟