Amphiumas

(Amphiumidae)

Class Amphibia

Order Caudata

Suborder Salamandroidea

Family Amphiumidae

Thumbnail description
These are elongate, cylindrical, medium-sized to very large semilarval salamanders with very short limbs and one to three toes per limb, no eyelids, and a gill slit is present in the pharyngeal region; fertilization is internal

Size
Adults reach 13–46 in (33–117 cm) in length, depending on the species

Number of genera, species
1 genus; 3 species

Habitat
Streams, lakes, ditches, ponds, swamps, and marshes

Conservation status
Not threatened

Distribution
Southeastern Virginia to eastern Texas along the coastal plain and northeast to southeastern Missouri in the Mississippi Valley drainage

Evolution and systematics

Amphiumidae dates from the Upper Cretaceous and Amphiuma from the Upper Paleocene, but the fossil record does not give a clear picture of the evolution of the family. Concise phylogenetic placement of the family has not been possible, despite various external and internal structural features, specific muscles present or absent, chromosome numbers and appearance, and biochemical studies. Electrophoretic analysis shows that the living species A. means and A. tridactylum have considerable genetic similarity, but A. pholeter is genetically quite distinct from the two larger species. When larval characteristics are not considered, different cladograms show that the relationships of Amphiumidae to Dicamptodontidae and Proteidae change positions. Amphiumidae is placed in the salamander suborder Salamandroidea based on several structural features of living species, but other features that might be considered are not available from the fossil material. The fact that the family members are semilarval in construction also is an obstacle to phylogentic interpretation. Fossils of A. means are known from Florida, and a questionable fossil of this species is known from Texas, well out of its current range. Amphiuma contains the longest and most massive salamanders in the United States. Local people use colloquial names, such as congo eel, lamper eel, ditch eel, lamprey, and congo snake with reference to the salamander. Amphiuma has legs and eyelids and lacks fins, whereas eels are legless and have fins and eyelids; the lack of scales in the congo snake preclude the validity of such a name. No subfamilies are recognized.

Physical characteristics

Amphiumas are elongate, cylindrical, eel-like salamanders with four small limbs that are usually less than 0.4 in (1 cm) long. They have one to three toes on each foot, depending on the species. The head is pointed, and the snout is somewhat depressed in two species. The tail is laterally compressed and makes up about 20–25% of the total body length. Adults have glandular skin that exudes slippery mucus. Metamorphosed individuals retain some larval features—lack of eyelids and tongue and presence of four gill arches with a single spiracular opening between the third and fourth arches. Lungs are present, but amphiumas also can breath via the pharynx and skin. When the young hatch, they retain gills for a few days. Hatchlings are a little more than 2 in (5.1 cm) in length, and metamorphosed individuals

may be as short as 2.3 in (5.8 cm). Adults reach 46 in (117 cm) in length. The trunk contains 57–60 costal grooves, each of which indicates a vertebra. The vertebrae are amphicelous, that is, they are concave on each end. A few anterior vertebrae bear ribs. Teeth are present on the premaxillary, maxillary, vomerine, and mandibular bones. A lateral line system is present on the body and head. The diploid chromosome number is 28. The dorsum is dark reddish brown to gray or black, and the belly may contrast with the dorsum or be almost as dark.

Distribution

These animals are found from southeastern Virginia southward along the coastal plain and throughout Florida, westward along the coastal plain; and from southwestern Alabama and all of Mississippi and Louisiana to the easternmost part of Texas and most southeastern part of Oklahoma northward to the extreme southeastern portion of Missouri. During the Cretaceous and the Upper Miocene, amphiumids were distributed widely in the United States, but since the Pleistocene, they have been restricted to their present ranges.

Habitat

These animals normally are aquatic and nocturnal. They are especially common in swamps, ditches, lakes, and sluggish streams, and one species typically is found in watery muck. They can be quite common in cities, where they occur in ditches and canals, including situations where the water is temporary. They may hide among aquatic plants but prefer crayfish holes. In rainy weather they may crawl around on wet surfaces.

Behavior

If a ditch or pond goes dry, amphiumids hide in holes where they can estivate; they have been excavated from as deep as 3.3 ft (1 m). They can go for up to three years without food and are known to live at least 27 years. They may lie in wait for passing prey or prowl in search of prey. The skin is shed periodically and may be eaten, thus helping to sustain them. Adult males may fight during the reproductive season, and many show scars from fighting. Locomotion is via lateral undulations. The animals are sensitive to vibrations that are likely detected by the lateral line system. Animals out of water occasionally emit a whistling sound. The mud snake (Farancia abacura) feeds almost exclusively on amphiumas. These salamanders can be captured with dip nets, seines, minnow traps, electroshock equipment, and by hand. The skin is so slippery that cotton gloves must be used to keep hold of the animal long enough to place it in a container. Care in handling is recommended, because the bite can be painful.

Feeding ecology and diet

Most activity takes place when water temperatures are above 41°F (5°C). The salamanders are strictly carnivorous and eat worms, aquatic insects and aquatic insect larvae, frogs, salamanders, fishes, and any other small vertebrates. A favorite prey is crayfish. Amphiumas normally wait in holes for passing prey, with the front part of the body protruding. The strong teeth and powerful bite assist in subduing prey. Amphiumas are preyed upon mostly by snakes and large wading birds.

Reproductive biology

Females have smooth cloacal walls, and males have papillae lining the walls. During the breeding season the male cloaca is swollen. Males may fight during the courtship season, and, as a result, they may show scars on the body. Spermiogenesis occurs from October to May. Courtship has been observed in one species. The female makes a nest in a moist place, usually under logs, leaves, or other cover. The eggs are laid in rosary-like strings with constrictions between each egg. Fifty to 200 eggs usually constitute a clutch, but as many as 354 eggs might be produced. The female coils around and guards the eggs. Incubation of eggs may take up to six months. The eggs and their gelatinous outer layers are approximately 0.4 in (1 cm) in diameter in large species. Nests in Florida have been found in the nest mounds of alligators. Females apparently reproduce biennially and males annually.

Conservation status

No species of Amphiumas are listed by the ICUN. Although human activity has decimated much of the habitat of Amphiuma, it also has increased habitat by the building of aquatic sites, ponds, ditches, canals, lagoons, and lakes. Amphiumas can survive in waters with fish, and they may be major predators in some aquatic habitats. Apparently, amphiumas are not now in need of protection, except for A. pholeter, which is scarce and restricted to a small area.

Significance to humans

Amphiuma flesh is edible and tastes much like frogs' legs. Few people eat them, because the skin is difficult to strip from the flesh. Amphiuma cells, especially the red blood cells, are the largest known in vertebrates, and they have long been used in physiological studies and in the classroom. The chromosomes also are very large and useful for study. The bite of amphiumas is considered to be poisonous by some rural inhabitants.

Species accounts

List of Species

Two-toed amphiuma

Amphiuma means

taxonomy

Amphiuma means Garden, 1821, Charleston, South Carolina, United States.

other common names

German: Zweizehen-Aalmolch; French: Amphiume.

physical characteristics

This large species reaches 46 in (117 cm) in length. The snout is somewhat depressed. The dorsum is usually dark reddish brown, black, or gray and contrasts little with the venter. A faint dark patch is present on the throat.

distribution

This species is distributed widely in the southeastern United States along the coastal plain from southeastern Virginia to southeastern Louisiana, including all of peninsular Florida.

habitat

This large aquatic salamander inhabits swamps, lakes, ditches, and sluggish streams.

behavior

When it is active, this species swims by undulating movements. It estivates in holes.

feeding ecology and diet

Crayfish are the primary items eaten, but the species also feeds on other aquatic organisms.

reproductive biology

Spermiogenesis occurs from October to May. Fifty to 200 eggs usually constitute a clutch. Courtship has not been observed. Incubation of eggs may take up to six months. Hatchlings are

about 2 in (5.1 cm) in length, and metamorphosed individuals may be as short as 2.3 in (5.8 cm). Females apparently reproduce biennially and males annually.

conservation status

The two-toed amphiuma is not threatened. No immediate conservation is needed for the species, but it is considered to be rare in several states and thus may warrant protection.

significance to humans

Like other members of the genus, this species is edible but rarely eaten, and it is used for classroom study.

One-toed amphiuma

Amphiuma pholeter

taxonomy

Amphiuma pholeter Neill, 1964, 4.5 mi (7.2 km) east-northeast of Rosewood, Levy County, Florida, United States.

other common names

None known.

physical characteristics

This is the smallest species of the Amphiumidae; adults reach only 8.5–13 in (22–33 cm) in total length. Each foot has a single toe. The entire body is dark reddish brown or gray to grayish brown with no notable contrast between dorsum and venter. The head is cylindrical, and the snout is not depressed.

distribution

The species has a narrow range in the coastal plain of southeastern Mississippi through the Florida panhandle and the northern part of the Florida peninsula to the extreme southern portion of Georgia in the United States.

habitat

Amphiuma pholeter lives primarily in the liquid muck of swampy streams and the swamps of smaller alluvial streams.

behavior

Little is known, but one might expect the species to behave similarly to the two larger species. This species is more likely to be an air breather, because of the anaerobic conditions of its mucky habitat.

feeding ecology and diet

Presumably, the diet is like that of other amphiumas, but its small size apparently limits its diet to small clams, earthworms, larval aquatic insects, and small beetles.

reproductive biology

Courtship apparently takes place in winter or spring, and the eggs are probably laid in June and July, with hatching in late summer or early fall. Because of the anaerobic habitat, the young may emerge from the eggs fully metamorphosed. Hatchlings reared in the laboratory reach adult size in about two years.

conservation status

The limited geographic distribution and relative rarity justify a need for protection. Georgia has placed the species under protection. Sediments from runoff in the course of home and road construction tend to destroy the muck habitats. Collecting also may be a detriment to the species.

significance to humans

None known.

Three-toed amphiuma

Amphiuma tridactylum

taxonomy

Amphiuma tridactylum Cuvier, 1827, New Orleans, Louisiana, United States.

other common names

None known.

physical characteristics

This species has three toes on each foot. The limbs of A. tridactylum are longer than those of A. means in relation to body length. In A. tridactylum the body is 35–37 times the length of the forelimbs, compared with 44–50 times in A. means, and the body is 22–25 times longer than the hind limbs compared with 31–34 times in A. means. Hatchlings are 1.7–2.5 in (4.3–6.4 cm) in total length, and metamorphosed individuals may be as short as 2.4 in (6.1 cm). Adults may reach 40.5 in (103 cm) in length. The dorsum is dark brown to black, and the venter is substantially lighter, thus creating a bicolor appearance. The throat has a conspicuous dark patch.

distribution

The species inhabits a narrow belt of eastern Texas less than 75 mi (122 km) wide and ranges from southeastern Oklahoma to southeastern Missouri and southwestern Alabama.

habitat

The three-toed amphiuma lives in swamps, lakes, ditches, and sluggish streams.

behavior

Although A. tridactylum generally stays in a restricted area, marked individuals have been known to move as far as 1,300 ft (396 m) from the original point of capture.

feeding ecology and diet

Crayfish are the primary items eaten, but the species also feeds on other aquatic organisms.

reproductive biology

The male courts the female by rubbing his snout against her. The female then rubs her nose along the male's body and coils her body under his, so that the two cloacae are joined. The male produces a spermatophore, and the female picks up the sperm with her cloaca. Examination of the female spermatheca shows that sperm is present throughout the year, but whether the sperm are fresh or carryovers from previous times is unknown. Egg development in female Amphiuma tridactylum occurs from November to September and spermiogenesis in the male from August to May. Females apparently have biennial egg-laying seasons. The eggs number 42–150 in salamanders from Louisiana, but examination of the ovaries indicates a potential for 106–354 eggs; the larger numbers are produced by larger females. Courtship and mating occur January to July and nesting from February to June in southeast Louisiana. Eggs are laid January to September. Hatching takes place from November to December, usually after a five-month incubation. One major study showed that most of the A. tridactylum eggs were laid in burrows. On one occasion a naturalist found a female with eggs retained in the body and well-developed larvae. A. tridactylum probably reach maturity in three to four years.

conservation status

The species is in no immediate danger, except in a few states where they are rare and warrant protection. Because A. tridactylum and A. means may occupy the same habitat, they may lend themselves to an interesting potential study of resource partitioning.

significance to humans

Like other members of the genus, this species is edible but rarely eaten, and it is used for classroom study. Several new species of flatworms (Trematoda) and tapeworms (Cestoda) taken from Amphiuma tridactylum have been described.

Resources

Books

Duellman, William E., and Linda Trueb. Biology of Amphibians. New York: McGraw-Hill Book Co., 1986.

Dundee, Harold A., and Douglas A. Rossman. The Amphibians and Reptiles of Louisiana. Baton Rouge: Louisiana State University Press, 1989.

Petranka, J. W. Salamanders of the United States and Canada. Washington, DC: Smithsonian Institution Press, 1998.

Periodicals

Baker, C. L. "The Natural History and Morphology of Amphiumae." Report of the Reelfoot Lake Biological Station 9 (1945): 55–91.

Cagle, Fred R. "Observations on a Population of the Salamander Amphiuma tridactylum Cuvier." Ecology 29, no. 4 (1948): 479–491.

Harold A. Dundee, PhD