Amphiuma is a genus of aquatic salamanders from the southeastern United States,

Taxonomy

Numerous phylogenetic studies have indicated that amphiumas form a clade with the families Rhyacotritonidae (torrent salamanders) and Plethodontidae (lungless salamanders), with an especially close relationship to Plethodontidae. Despite this possible relationship, the two families must have still diverged very early on. The genus Proamphiuma from the Cretaceous is the earliest known member of the family, and closely resembles the modern species aside from less elaborate vertebral structures.

Description

Amphiumas have an elongated body, generally grey-black in color. They do have legs, but they are merely vestigial and very small. While amphiumas can be up to long, their legs measure only up to about . It is because of this that they are often mistaken for eels or snakes. They also lack eyelids and a tongue. Amphiumas also have a lateral line visible on the sides of their bodies, which is capable of detecting movement and is used in aid of hunting.

Female amphiumas lay their eggs in wet mud, and then remain coiled around them for about five months, until they hatch. The larvae have external gills, but after about four months these external gills disappear and the lungs begin to work. One pair of gill slits is retained and never disappears, so the metamorphosis remains incomplete.

Species

There are three extant amphiuma species,

Food habits

The amphiuma's predatory behaviors and food selection are very calculated and variable depending on abundance of food. In addition to eating frogs, snakes, fish, crustaceans, insects, and other amphiuma, amphiuma have been found to eat annelids, vegetables, arachnids, mollusca, and larvae. Amphiuma seem to have a preference for eating crawfish. It has been documented that amphiuma will pass on smaller crawfish in order to consume larger ones. It is suggested that this limits wasting energy in pursuing prey with less caloric density. In captivity, the predatory behavior amphiuma display depends on the presence or lack of food. Amphiuma will remain inactive when food is absent, and will become more active once food has been introduced into their habitat. Stationary suction feeding involve little to no movement where it opens the mouth with buccal expansion but no forward movement of the body. The muscles of the jaw give them the ability to grab and hold on to prey as well as create a negative pressure to suck in the prey and displace the jaw. Muscles of note in the amphiuma include: the levator mandibulae anterior and levator mandibulae externus, which elevate the lower jaw of the amphiuma while the depressor mandibulae depresses the lower jaw. The intermandubularis works by tensing the mouth floor. The branchiohyoideus and geniohyoideus draws the hyoid arch which causes the suction and displacement. Their lungs are long organs, extending over half of the body length, with dense capillary networks and large surface area that suggest the utilization of the entire lung for respiration while the animal is in water or on land. This is suggested by the high lung to respiratory capillary density compared to the relatively low skin to respiratory capillary density. Generally, males have been found to possess larger bodies and longer heads compared to the female sex, which normally is indicative of male-male combat observed within the population. There has been, however, no other physical indicating factors for male-male combat as in other species of amphibians, such as horns or spines.

Amphiumas may be sexed as male or female based on the pigmentation of the cloacal opening. Males exhibit white or pink coloration while females exhibit dark pigmentation. Occasionally, males may demonstrate partial pigmentation, but never have full dark coloration like that of females.

References

  • Tree of Life: Amphiumidae
  • amphiumas.org