Aquatic larvae resemble adults except that they have filamentous external gills, four pairs of gill slits and their tail is more finlike. Larvae inhabit ponds or slow streams and usually can be found throughout the year. The morphological characters given below are the ones standardly used to diagnose the salamander family Ambystomatidae and to assess its phylogenetic relationships to other salamanders. The individual characteristics are in most cases shared with other salamanders and should not be interpreted as synapomorphies of the Ambystomatidae. The premaxilla consists of separated, paired bones.
Maxillary bones are present and well developed.
Bilaterally paired septomaxillary bones are present. Lacrimal bone is absent. Quadratojugal bone is absent. Pterygoid bones are present. An internal carotid foramen is present in the parasphenoid bone in some species.