Unlike a metamorphosed salamander, a neotenous one retains external gills and a tail and body fin, lacks moveable eyelids, and of course is obligatorily aquatic.

This also occurs naturally under favorable conditions, in its native localities; although it commonly lives and breeds in a larval state, with persistent external gills.

The external gills are moderately long, slender, and filamentous; the yolk sac is still moderately large.