A completely aquatic salamander shaped like a long cylinder with a somewhat pointed head; it has tiny gray eyes and very small fore- and hind limbs. Each limb has three very small toes. The dorsal color is dark brown or black; the belly is lighter brown or gray. Adults do not have gills, but a gill slit is present on each side of the head. Amphiumas have lungs and must breathe air at the surface of the water. Note that amphiumas often are missing toes or entire limbs. Amphiumas are alert, fast, and slippery and may bite viciously if captured.
Similar species: The western lesser siren (Siren intermedia nettingi) has feathery external gills and lacks hind limbs; in Missouri, its range extends farther north and east than the amphiuma’s. Both of these salamanders can be distinguished from eels and lampreys (which are fish) by their limbs with fingers, tiny eyes, and lack of fins and scales.