There are four species of sirens, all found in the southern United States and northern Mexico. Sirens are fully aquatic, with external gills and streamlined bodies. They have no hind limbs. Siren species can be relatively small to large, from 10 to 90 centimeters long. They live in shallow, slow-moving waters and eat invertebrates that they suck into their mouths. Sirens are considered the most primitive group of salamanders still living.
Tanya Dewey (author), Animal Diversity Web.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.