Description
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).

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.

Distribution and Habitat

Country distribution from AmphibiaWeb's database: United States

U.S. state distribution from AmphibiaWeb's database: Alabama, Arkansas, Kentucky, Louisiana, Missouri, Mississippi, Oklahoma, Tennessee, Texas

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (12 records).

Amphiuma tridactylum occurs in Coast Plain habitats from eastern Texas to western Alabama, and the range extends northwards up the Mississippi Valley to southeastern Missouri and extreme western Kentucky. This species prefers permanent or semi-permanent aquatic habitats with abundant vegetation. Individuals may be found in drainage ditches, swamps, sloughs, sluggish streams, and semi-permanent ponds (Petranka 1998).

Life History, Abundance, Activity, and Special Behaviors
Courtship and mating occur primarily in the winter and spring months, although it may occur through the summer as well (Petranka 1998). Courtship and mating occur under water, and activity is greatest at dawn and dusk. Fertilization is internal and sperm transfer occurs by cloacal apposition (Baker et al. 1947).

Males reproduce annually, while females likely reproduce biannually. Females lay from 42 - 131 (mean 98) eggs, and brood the eggs until hatching. Nests of A. tridactylum have been found under logs and other cover objects at the edges of ponds and swamps. Hatching occurs in the late summer to late autumn, after a 4-5 month developmental period. See Petranka (1998) and references therein.

Animals are active primarily at night, retreating to burrows during the day. Some animals forage by sticking only the head and upper body from the burrow. Diet items include crayfish and earthworms primarily, but also fish, spiders, snails, and aquatic and terrestrial insects. Predators include cottonmouth (Agkistrodon), and mudsnakes (Farancia). Amphiumas are capable of delivering a powerful bite, and this is their main defense against predators and people. During dry periods and droughts amphiumas can remain in their burrows for many months without feeding. Animals will also move overland during extremely wet periods. Three-toed amphiumas are locally common in many areas. See Petranka (1998) for references.

Three-toed amphiumas are likely to play the role of top predator in many aquatic systems. The degree to which they affect community structure is not known and would be a productive area of investigation, particularly because the wetland habitats where they occur are threatened with continuing loss (Petranka 1998).

Larva
Hatchling size is 43-64 mm total length. Juvenile coloration is lighter than adults. Juveniles possess short, whitish gills which are resorbed a few weeks after hatching. Legs are well developed at the time of hatching. See Petranka (1998) and references therein.

Trends and Threats
Three-toed amphiumas are fairly flexible in the sorts of aquatic habitats they will occupy and have adapted to man-made water courses and drainage ditches. However, the increasing destruction of wetland habitats is a potential threat to many populations (Petranka 1998).

Comments
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.

References

Baker, C. L., Baker, L. C. and Caldwell, M. F. (1947). ''Observation of copulation in Amphiuma tridactylum.'' Journal of the Tennessee Academy of Science, 22, 87-88.

Karlin, A. A., and Means, D. B. (1994). ''Genetic variation in the aquatic salamander genus Amphiuma.'' American Midland Naturalist, 132, 1-9.

Petranka, J. W. (1998). Salamanders of the United States and Canada. Smithsonian Institution Press, Washington D.C. and London.

Salthe, S. N. (1973). ''Amphiuma tridactylum Cuvier. Three-toed Congo Eel.'' Catalogue of American Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles, 149.1-149.3.

Salthe, S. N. (1973). ''Amphiumidae. Amphiuma.'' Catalogue of American Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles, 147.1-147.4.

Species Account Citation: AmphibiaWeb 2022 Amphiuma tridactylum: Three-toed Amphiuma <https://amphibiaweb.org/species/3855> University of California, Berkeley, CA, USA. Accessed Nov 22, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 Nov 2024.

AmphibiaWeb's policy on data use.