The Characteristics of Caecilians
Investigating the Traits of Order Gymnophiona
As they are rarely seen, the biology of caecilians is largely unknown. Most of the knowledge about them is derived from observations made during capture or from captive or museum specimens.
The Diversity and Distribution of Caecilians
Caecilians occur worldwide in the tropics, except for Madagascar and Papua-Australia but are most numerous in the tropical forests of South America, Africa, and Southeast Asia.
In spite of their widespread occurrence, there are only about 160 species of these strange and seldom-seen amphibians which zoologists have divided into six families.
The Body Plan of Caecilians
Caecilians (also known as “rubber eels”) are legless, wormlike burrowers that feed on worms and other soil invertebrates. Except for a few aquatic species, most caecilians are fossorial (adapted for digging and burrowing) living in moist soils often adjacent to streams, lakes, and swamps. The blunt heads of these animals are digging tools for creating the burrows in which they live.
The members of order Gymnophiona (Gr. gymnos, naked + ophineos, as a snake) range in size from 10-150 cm (4-60 inches) and their smooth skin varies from blackish to pinkish tan.
Some types have small calcite scales embedded in the skin. Caecilians appear to be externally segmented but this is superficial, caused by folds in the skin that overlie separations between muscle bundles.
Owing to their underground life, their eyes are small and covered by skin for protection giving rise to the misconception that caecilians (L. caecus = blind) are blind. This is not the case but their visual sense is limited to simple light-dark perception.
Caecilians possess two retractable sensory tentacles on their head. By possibly transporting chemicals from the environment to olfactory detector cells in the roof of the mouth, these tentacles are thought to function in a secondary olfactory capability in addition to the normal sense of smell based in the nose.
Except for one lung-less species, caecilians are lung breathers, but they also use the skin and the smooth skin lining the mouth for oxygen absorption. Often the left lung is much smaller than the right one, an adaptation to an elongated body shape that is also found in snakes.
Fertilization in caecilians is internal and effected by an extendible male copulatory organ known as the phallodeum.
Caecilians Produce Potent Skin Poisons
Recent research has found that certain caecilians produce potent skin poisons from specialized skin glands. These poisons most likely prevent predation. In fact, the poison of the bright yellow caecilian (Schistometopum thomense) of West Africa kills other animals kept in the same tank within a few days.
Chemical analysis has shown that these poisons are very different from those of other amphibians such as those produced by the poison-dart frogs.
With their secluded life style and secretive habits, the strange wormlike caecilians are largely unknown and unappreciated by the bulk of humanity.
Additional Articles
- The Characteristics of Salamanders investigates the diversity, distribution, and body plan of the tailed amphibians – the salamanders.
- The Characteristics of Frogs and Toads investigates the diversity, distribution, and body plan of the most familiar and recognizable of the amphibians – frogs and toads.
The Blunt Head of a Caecilian
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Aquatic Caecilians
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