Caecilians are found in most of the tropical regions of South-East Asia, Africa, and South America, except the dry areas and high mountains.
The taxonomy of Chondrichthyes reveals both the connectedness of living organisms and the diversity in nature.
Caecilians are the only amphibians with dermal scales; these scale-like structures are more similar to fish scales than reptile scales.
The male Caecilians have an external organ, the phallodeum, which is inserted into the cloaca of the female for two to three hours.
In Africa, caecilians are found from Guinea Bissau (Geotrypetes) until Northern Zambia (Scolecomorphus).
Except for one lungless species—Atretochoana eiselti, only known from a single specimen collected somewhere in South America—all Caecilians have lungs, but also use the skin or the mouth for oxygen absorption.
The skin of caecilians is smooth and usually dark-matte, but some species have colorful skins.
Limbs and limb girdles are absent in all living caecilians.
Caecilians have degenerate feet, making the smaller species resemble worms, while the larger species with lengths up to 1.5 m resemble snakes.
All caecilians share two tentacles at their head, which are probably used for a second olfactory capability in addition to the normal sense of smell based in the nose.
Taxonomically, the caecilians commonly are divided into five or six families.
No studies have been made in central Africa, but it is likely that caecilians are found in the tropical rainforests there.
Caecilians are the only order of amphibians that only use internal insemination.
Caecilians reveal how difficult it is to place the vast diversity of nature into discrete taxonomic boxes based on anatomical features, as well as the importance of common lineage in establishing scientific classification.
A Swiss researcher Daniel Hofer has found that certain caecilians produce potent skin poisons from specialized poison glands.
Lacking limbs, caecilians resemble earthworms or snakes in appearance.