Comprehensive DescriptionRead full entry
A large, eel-like aquatic salmander. Like other members of the family Amphiumidae, three-toed amphiumas have tiny limbs, a single gill slit, no external gills, and no eye lids (Salthe 1973; Petranka 1998). Amphiuma tridactylum, as the name suggests, has three toes on each foot. Coloration of this species is more distinctly bicolored than other amphiumas. The dorsum is black, slate gray, or brownish, while the venter is light gray. A dark patch is present on the chin and throat region. Adults reach 46 to 106 cm total length, with 57 to 60 costal grooves. The tail is laterally compressed and comprises about 25% of the total length (Salthe 1973; Petranka 1998).Hatchling size is 43-64 mm total length. Juvenile coloration is lighter than adults. Juveniles possess short, whitish gills which the resorb a few weeks after hatching. Legs are well developed at the time of hatching. See Petranka (1998) and references therein.
The three species of Amphiuma are similar but can be differentiated based on the number of toes (one, two, or three), coloration, and body size.
Amphiuma tridactylum and A. means are genetically similar, while A. pholeter is quite distinct and represents an ancient evolutionary offshoot (Karlin and Means 1994). Some authors have argued that A. means and A. tridactylum should be treated as conspecifics. These species, which are sympatric over much of their ranges, differ in coloration, number of toes, and some body proportions. See Salthe (1973) for discussion of this issue.