Vertebrate Zoology: A Tutorial Guide - T. A. Dauda 2014

Metazoa
Fishes
Class Amphibia — Order Apoda (Gymnophiona)

The order of caecilians comprises about 60 species of amphibians inhabiting mainly South America, parts of Tropical Africa, and southern Asia. Members of this order have a worm-like body with annular constrictions. Limbs are absent, and the tail is short. The Skin is smooth yet rich in mucus-secreting glands. Fertilization is internal. Caecilians lead a burrowing lifestyle, feeding on soil invertebrates. Typical representatives include the ringed caecilian and the Ceylon caecilian, which measure about 40 cm in length. Caecilians inhabit damp environments and are capable of burrowing into the soil to a depth of 20–50 cm. During the breeding season, females lay up to 30 fertilized eggs in subterranean burrows or

under stones, coiling around them to prevent desiccation. The larvae that hatch from the eggs migrate to a body of Water, where they complete their development.

QUESTIONS FOR SELF-assessment and review:

1. Where do amphibians live?

2. What general structural and organizational features characterize the Class Amphibia?

3. What transformations do larvae undergo during their development?

4. What structural and behavioral features characterize the Representatives of the orders: Urodela (tailed amphibians), Anura (tailless amphibians), and Gymnophiona (caecilians)?

5. What is THE ECOLOGICAL AND economic significance of amphibians in nature and for humans?

ORIGIN AND EVOLUTION of Amphibians

The earliest amphibians—the ichthyostegids—diverged from freshwater lobe-finned fish. Their remains have been discovered in Upper Devonian deposits in Greenland. At the end of the Devonian, three distinct branches of amphibians, formerly grouped under the collective term stegocephalians, branched off from the ichthyostegids. One of these branches gave rise to modern tailed and limbless amphibians, another to tailless amphibians, and the third branch gave rise to primitive reptiles.