COECILIA, a genus of limbless, worm-like amphibians (see AMPHIBIA), first described by Linnaeus as a group of snakes, but now recognized as of a distinct order of Amphibia to which the names apoda, peromela, and Gymnophiona have been given. The latter is now in general use by systematists, but the order is sometimes popularly called Coecilia.
The coecilians, or Gymnophiona, are all limbless, long-bodied Amphibia having a very short tail, the vent being nearly terminal. Their bodies are usually more or less ringed by a series of dermal folds which give their owners the appearance of large earthworms. Within these folds there are found in most genera a series of minute scales which distinguish the Gymnophiona from other Am phibia. All genera are characterized by a peculiar protrusible ten tacle on the side of the face near the nostril or eye. It is said to function as a tactile organ, but is radically different from such sense organs in other Amphibia. Coecilians are primitive forms apparently directly derived from the extinct lepospondylia. They show no close affinity to other living groups, and are more primi tive than other living Amphibia in possessing in certain genera a post-frontal (Ichthyophis, etc.), an ectopterygoid (Hypogeophis, etc.), a transitory spiracle cleft, a sixth gill sack, four pairs of functional thymus glands and two additional pairs of rudiments during development. Such apparently primitive structures as the unspecialized hyoid apparatus may owe their simplicity to sec ondary degeneration. In certain features of the skull the coecil ians resemble a partly metamorphosed urodele, such as Crypto branchus, but one highly modified for burrowing. The lidless eyes are usually indistinct and sometimes very degenerate and hidden under the bones of the skull. In spite of primitive characters of integument and skull the coecilians must be considered a highly aberrant and specialized group.
Nieden (1913), the latest reviewer of the order, recognizes nine teen genera and fifty-five species, all referable to a single family, the Coeciliidae. The primitive genera Ichthyophis, Rhinatresna, etc., possess scales, exhibit the fewest fusions of skull elements, and are the least modified for burrowing. The most specialized are either degenerate burrowers or aquatic (Typhlonectes) . In correlation with the habitat the structure of integument, skeleton, or lungs may be modified. The coecilians inhabit the tropics. They are seldom seen except after heavy rains or after ploughing the ground.
The life histories of several genera of coecilians are known. Ichthyophis lays its eggs on land in damp situations, the larvae escaping to take up an aquatic existence. The more specialized Hypogeophis skips over the larval stage. Finally the aquatic Typhlonectes retains its eggs within the oviduct and gives birth to living young. Other species may be oviparous, others viviparous.
(G. K. N.)