The Caecilian

Mar 13, 2011 Features / Columnists, Interesting Creatures in Guyana

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The caecilians are an order (Gymnophiona) of amphibians that superficially resemble earthworms or snakes. They mostly live in the ground, which makes them one of the least known orders of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda.
Caecilians completely lack limbs, making the smaller species resemble worms, while the larger species with lengths up to 1.5 metre (4 feet 11 inches) resemble snakes. The tail is short or absent, and the cloaca is near the end of the body.
Their skin is smooth and usually dark-matte, but some species have colourful skin. Inside the skin are calcite scales. The skin also has numerous ring-shaped folds, or annuli, that partially encircle the body, giving them a segmented appearance. Like other living amphibians, the skin contains glands that secrete a toxin to deter predators.
Caecilians’ vision is limited to dark-light perception, and their anatomy is highly adapted for a burrowing lifestyle. They have a strong skull, with a pointed snout used to force their way through soil or mud.
In most species, the number of bones in the skull are reduced and fused together, and the mouth is recessed under the head. Their muscles are adapted to pushing their way through the ground, with the skeleton and deep muscles acting as a piston inside the skin and outer muscles. This allows the animal to anchor its hind end in position, and force the head forward, and then pull the rest of the body up to reach it in waves. In water or very loose mud, caecilians instead swim in an eel-like fashion.
Caecilians in the family Typhlonectidae are aquatic as well as being the largest of their kind. The representatives of this family have a fleshy fin running along the rear section of their body, which enhances propulsion in water.
All but the most primitive caecilians have two sets of muscles for closing the jaw, compared with the single pair found in other creatures. These are more highly developed in the most efficient burrowers among the caecilians, and appear to help keep the skull and jaw rigid.
Adapting to their underground life, the eyes are small and covered by skin for protection, which has led to the misconception that they are blind. This is not strictly true, although their sight is limited to simple dark-light perception.
All caecilians possess a pair of tentacles, located between their eyes and nostrils. These are probably used for a second olfactory capability, in addition to the normal sense of smell based in the nose. Except for two lungless species — Atretochoana eiselti and Caecilita iwokramae — all caecilians have lungs, but also use the skin or the mouth for oxygen absorption. Often the left lung is much smaller than the right one, an adaptation to body shape that is also found in snakes.
These amphibians are found in wet tropical regions of Southeast Asia, India and Sri Lanka, parts of East and West Africa, the Seychelles islands in the Indian Ocean and in northern and eastern South America. In South America they extend through subtropical eastern Brazil well into temperate northern Argentina.
Caecilians are the only order of amphibians that use internal insemination exclusively. The male caecilians have a penis-like organ, the phallodeum, which is inserted into the cloaca of the female for two to three hours. About 25 percent of the species are oviparous (egg-laying); the eggs are guarded by the female.
For some species the young caecilians are already metamorphosed when they hatch; others hatch as larvae. The larvae are not fully aquatic, but spend the daytime in the soil near the water.
Seventy-five percent of the species are viviparous, meaning that they give birth to already developed offspring. The fetus is fed inside the female with cells of the oviduct, which they eat with special scraping teeth.
The egg-laying species Boulengerula taitanus feeds its young by developing an outer layer of skin, high in fat and other nutrients, which the young peel off with similar teeth. This allows them to grow by up to 10 times their own weight in a week. The skin is consumed every three days, the time it takes for a new layer to grow, and the young have only been observed to eat it at night. It was formerly thought that the juveniles subsisted only on a liquid secretion from their mother.
Some larvae are born with enormous external gills which are shed almost immediately while some Caecilian are oviparous and known to show maternal care, with the mother guarding the eggs until they hatch.
The diet of caecilians is not well-known. Mature caecilians seem to feed mostly on insects and other invertebrates found in the habitat of the respective species. Caecilians in captivity can be easily fed with earthworms, and worms are also common in the habitat of many caecilian species.
(Source: Wikipedia – The Free Online Encylopedia)

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