This salamander is sexually dimorphic. Both male and female have black dorsal ground coloring; the bands on the female are gray or silver, and those on the male are white. the sides and the venter are black as well. They are generally short-tailed, stocky and broad-headed (Bartlett & Bartlett 1999).

A. opacum is the most strongly dimorphic of the ambystomatids. They are capable of burrowing, but they rather remain closer to the surface except for seasons of extended drought (Bartlett & Bartlett 1999).