Caecilian
From Freepedia
- See also: Caecilian, bishop of Carthage, 312 C.E.
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Rhinatrematidae |
The Caecilians are an order (Gymnophiona or Apoda) of amphibians which resemble worms or snakes. They mostly live hidden in the ground which makes them the least explored order of amphibians, and widely unknown.
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Anatomy
Caecilians' feet have degenerated, making the smaller species resemble worms, while the larger species with lengths up to 1.5 m resemble snakes. The tail is also very short, so the cloaca is near the end of the body. Their skin is smooth and usually dark-matt, but many species also have colorful skins. Inside the skin are calcite scales, which suggests that they are related with the fossil Stegocephalia. However the scales are now believed to be a secondary development, and not directly inherited from Stegocephalia. Due to their underground life the eyes are small and covered by skin for protection, which have led to the misconception that they are blind. However due to the skin cover their visual sense is limited to simple dark-light perception. 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.
Except for one lungless species - Typhlonectes eiselti, only known from one specimen collected somewhere in South America - 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 also found in snakes.
Distribution
Caecilians are found in most of the tropic areas of South-East Asia, Africa and South America, except the dry areas and the high mountains. In South America their distribution extends well into the temperate north of Argentina. For central Africa no systematic search has been done yet, but it is likely Caecilians are found all over the tropical rainforest there.
Reproduction
Caecilians are the only order of amphibians which only use internal insemination. The male Caecilians have a penis-like organ, the phallodeum, which is inserted into the cloaca of the female for 2 to 3 hours. About 25% of the species are oviparous (egg-laying); the eggs are guarded by the female. For some species the young Caecilians are already metamorphed when they hatch, other hatch as larvae. The larvae aren't fully aquatic, but spend the daytime in the soil near the water.
75% of the species are viviparous, meaning that they give birth to already developed offspring. The fetus is fed inside the female with special cells of the oviduct, which are eaten by the fetus with special scraping teeth.
Origin of the name
The name Caecilian derives from the Latin word caecus = blind, referring to the small or sometimes non-existing eyes. The name dates back to the taxonomic name of the first species described by Carolus Linnaeus, which he gave the name Caecilia tentaculata. The taxonomic name of the order derives from the Greek words γυμνος (gymnos, naked) and οφις (ophis, snake), as the Caecilians were originally thought to be related with snakes.
Taxonomy
Taxonomically the Caecilians are divided into 5 families. The species numbers have to be taken with care, as many of these species are identified on the basis of only one specimen. It is likely that not all species have been described yet, and some of the species described below as different may be combined into one species in a future reclassification.
- Beaked Caecilians (Rhinatrematidae) - 2 genera, 9 species
- Fish Caecilians (Ichthyophiidae) - 2 genera, 39 species
- Indian Caecilians (Uraeotyphlidae) - 1 genus, 5 species
- Tropical Caecilians (Scolecomorphidae) - 2 genera, 6 species
- Aquatic Caecilians (Typhlonectidae) - 5 genera, 13 species
- Common Caecilians (Caeciliidae) - 26 genera, 107 species
Misc
Large Caecilians dubbed "ingots" plagued the French occupation of Indochina in the years before the Vietnam war. The creatures were reported to burrow large holes and disrupt troop movement.
References
- Werner Himstedt, Die Blindwühlen, ISBN 3894324341 (German)
