Amphibians
Amphiuma
Amphiumidae · also called congo eel, conger eel, lamper eel
An amphiuma is a salamander pretending to be an eel. Its body is long, dark, slick, and finless, and its four legs are so small — a few millimetres, with as few as one toe each — that you can hold one and not notice them. It lives in the swamps of the American Southeast, bites like a snapping turtle if you grab it, and carries some of the largest cells of any land animal.
Overview
Amphiumas are the family Amphiumidae, just three species, all in the coastal plain of the southeastern United States. They are large, eel-like aquatic salamanders — the two-toed amphiuma can exceed a metre — with a scaleless dark body, four tiny useless legs, and a strong bite. They are night-hunting carnivores of swamps, ditches, and sloughs, taking crayfish, worms, fish, frogs, and each other.
Stuck between two body plans
An amphiuma undergoes a partial metamorphosis: it loses its external gills but keeps one gill slit open for life, and it has lungs but no eyelids and reduced eyes. It sits between the permanently larval salamanders like the siren and the fully land-going ones.
Big cells, hard bite
Amphiuma red blood cells are roughly 25 times the volume of a human’s — among the largest of any animal — which, with the huge genome, makes amphiuma tissue a standard teaching specimen. And unlike almost every other salamander, a large amphiuma can give a person a deep, bloody bite.
Drought and long life
When its swamp dries, an amphiuma burrows into the mud and can cocoon itself in dried skin for weeks or months. Amphiumas live more than 25 years, breed at most every other year, and the female coils around her eggs for four to five months.
Status
Amphiumas as a family are Not Evaluated. The two-toed and one-toed species are reasonably secure across the southeastern coastal plain, though all three depend on shallow, warm, weedy, fish-poor wetlands that are widely drained, ditched, and polluted.
Amphiuma: common questions
Is an amphiuma an eel?
No. Despite common names such as congo eel, conger eel, and lamper eel, an amphiuma is a salamander, and therefore an amphibian, not a fish. The eel names come from its long, cylindrical, scaleless, dark body and its aquatic life, which make it look eel-like at a glance, especially since its four legs are so tiny they are easy to miss. But an amphiuma has amphibian features, including moist glandular skin, lungs, a gill slit rather than true gills or fins, and amphibian eggs laid in a burrow and brooded by the female. Real eels are bony fish with gills, fins, and a completely different anatomy.
Why do amphiumas have such tiny legs?
The legs are a vestige, retained from a four-legged ancestor but reduced almost to nothing because the amphiuma has fully committed to an eel-like way of moving. Swimming and burrowing through mud with side-to-side body waves is efficient in the amphiuma's dense, weedy, soft-bottomed habitat, and legs of any useful size would get in the way. The result is two pairs of limbs only a few millimetres long, tipped with one, two, or three toes depending on the species, which cannot bear the animal's weight and play no real part in getting around. Several other aquatic salamander groups, such as the sirens, have gone even further and lost the hind legs entirely.
Do amphiumas really bite hard?
Yes, for a salamander they bite exceptionally hard. Amphiumas are muscular, quick, and equipped with strong jaws and small sharp teeth, and a large two-toed amphiuma, which can exceed a metre in length, will thrash and bite repeatedly if grabbed. The wound is a deep puncture-and-tear that bleeds freely and has been likened to the bite of a small snapping turtle, and it can become infected. Field biologists handle large amphiumas with thick gloves and a firm grip behind the head. This is unusual, since the great majority of salamanders are harmless and rely on toxins in the skin rather than biting.
What is special about amphiuma cells?
Amphiumas, along with a few other salamanders and lungfish, have unusually large cells and an enormous genome. Their red blood cells are among the largest known, with a volume around 25 times that of a human red blood cell, and are visible almost as specks. Because the cells and their nuclei are so big, and the chromosomes correspondingly large, amphiuma tissue is a classic teaching and research material for looking at cell structure, mitosis, and chromosome organisation under a light microscope. The large genome is thought to be linked to the animal's slow metabolism and slow pace of life rather than to greater complexity.