Amphibians
Two-toed Amphiuma
Amphiuma means · also called two-toed amphiuma, congo eel, conger eel, lamper eel, ditch eel
The two-toed amphiuma is a salamander doing an impression of an eel — a slippery, metre-long, mud-dwelling predator of Southern swamps whose four legs are so tiny you could hold one and not notice them. It has some of the biggest cells of any animal, and, unusually for a salamander, a bite that can leave a scar.
Overview
Two-toed amphiumas live in swamps, sloughs, ditches, and slow mud-bottomed streams of the southeastern US coastal plain. They are fully aquatic, nocturnal, and spend the day in burrows or under debris, hunting crayfish — the mainstay of their diet — along with fish, frogs, snakes, and other amphiumas. They keep a pair of gill slits but breathe mostly by surfacing to gulp air.
Eel in name and shape only
The folk names — congo eel, conger eel, ditch eel — are all wrong: it is an amphibian, native to the American South, not a fish and nothing to do with the Congo. The eel look comes from a long body and near-lost limbs, all for moving through mud and weed by undulation. Each of the four legs is a centimetre or two long with two toes.
Giant cells
The two-toed amphiuma has one of the largest genomes of any animal — about 25 times a human’s — and correspondingly enormous cells and nuclei, which made it a classic cell-biology model for studying chromosomes and cell division.
Surviving drought
When a swamp dries, the amphiuma burrows into the mud and forms a slime cocoon, surviving about three years dormant until water returns.
A real bite
Unusually for a salamander, a large amphiuma has a strong bite and sharp teeth and will bite hard if grabbed or stepped on — deep enough to bleed and scar. It is not venomous, but it should be left alone.
Status
The two-toed amphiuma is Least Concern, common in suitable southeastern wetlands.
Two-toed Amphiuma: common questions
Is the "congo eel" an eel, and does it come from the Congo?
Neither. Despite folk names like congo eel, conger eel, lamper eel, and ditch eel, the two-toed amphiuma is a salamander — an amphibian — native to the wetlands of the southeastern United States, with no connection to the Congo or to true eels (which are fish). The eel-like appearance comes from its long, cylindrical, slippery body and its reduced fins-and-legs, all adaptations for moving through mud and dense vegetation by undulating like an eel. It keeps a pair of gill slits but breathes mainly by coming to the surface to gulp air, as its lungs do most of the work.
Why does it have those tiny useless legs?
The amphiuma's ancestors were normal four-legged salamanders, and as the lineage specialised for a burrowing, eel-like life in mud, the legs were progressively reduced rather than lost entirely. Each of the four legs on a modern two-toed amphiuma is only a centimetre or two long and ends in two vestigial toes; the three-toed and one-toed amphiumas have gone further. The legs play no meaningful role in swimming or crawling — the animal moves by whole-body undulation — but they have not been selected away completely, and they may still have a minor function in anchoring or manoeuvring in tight spaces.
Why is it important to science?
Because of its cells. The two-toed amphiuma has one of the largest genomes of any animal, roughly 25 times the amount of DNA in a human cell, and as a result its individual cells, and especially their nuclei, are enormous — large enough to see and manipulate easily under a microscope. This made the amphiuma a classic model organism in early cell biology and cytogenetics for studying chromosome structure, cell division, and nuclear organisation, and its red blood cells (also giant) are still used in physiology teaching and research. Why it, and some other salamanders and lungfish, carry so much DNA is not well understood.
Can it really bite you?
Yes, and among salamanders that is unusual enough to be worth stating plainly. Most salamanders are small, soft-mouthed, and harmless to handle. A large two-toed amphiuma is a muscular, metre-long predator with a strong bite and rows of sharp teeth, used on crayfish, fish, and other amphiumas, and it will bite hard if grabbed or trodden on, drawing blood and sometimes leaving a lasting scar. Anglers who catch one on a baited hook, and people who dig them out of drying mud, are the usual victims. It is not venomous and there is no lasting danger beyond the wound and infection risk, but it should be handled with respect or, better, left alone.