Caecilians look like worms or snakes but they are neither. They are more closely related to frogs and salamanders and are classified as amphibians. They do not resemble other amphibians because they have adapted to a burrowing life style, which has led to the loss of limbs and the almost complete loss of eyes. Caecilians are different enough from other amphibians to be classified in their own order, the Gymnophiona. The name caecilian comes from the Latin word for blind but in fact, most caecilians have limited vision in that their little eyes can distinguish between light and dark. They also have small tentacles in front of the eyes that they can use like feelers.
Caecilians lack legs and do not have pelvic or pectoral girdles, but this is a secondary loss and the few known fossil caecilians had very small legs. Some of the more aquatic species have small raised fins on their backs. All adult caecilians breathe air with lungs so the aquatic species must surface regularly. The body is elongated but the tail is very short. The body is arranged in rings called annuli, which give the animals their earthworm-like appearance. Most caecilians are small but a few may get as long as a hundred cm.
Caecilians have a subterminal mouth which has both jaws and small sharp teeth. They have a double set of jaw muscles whereas other vertebrates have only a single set. It is thought these are used to hold the mouth firmly closed when the animal is burrowing. The skin is unique among amphibians in having small scales. It can also contain poison glands, but it is not known how toxic the poison actually is.
The Gymnophiona are usually divided into three families: the beaked caecilians of South America (9 species in the family Rhinatrematidae); the fish caecilians of Southeast Asia (44 species, Ichthyophiidae); and the common caecilians (118 species, Caeciliidae) which are found across Africa and South America and Southern Asia. Common caecilians have even made it to the Seychelles Islands, but not to Australia.
Caecilians live in wet tropical forests, but are seldom seen because of their burrowing life style. They eat worms, insects and other invertebrates. They can lay eggs or bear live young. The larvae are aquatic and they breathe with gills. Like other amphibians, caecilians go through a metamorphosis to attain their adult forms. Their life spans are relatively long for such small animals, being from five to twenty years. Ground dwelling snakes are probably their primary predators.
Because caecilians are secretive, burrowing soil dwellers, little is known about most species. Some species are still known from only single specimens. Now that at least one aquatic species is kept as a pet, more information about their behavior should become available. They are at this point, however, a group of animals about which little is known and much is to be learned.
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