SURVEY OF AMPHIBIANS
Amphibians occur on all continents except Antarctica. There are three orders of amphibians: Caudata, (salamanders), Anura, ( frogs and toads) and Gymnophiona (caecilians).
ORDER CAUDATA (cauda, tail + Or. ara, to bear)
The characteristics are:
1. They possess a tail throughout life.
2. Both pairs of legs are present in them.
3. They lack middle ear.
4. They hav e 150 species.
Example: Salamander, newts
Habit and Habitat
115 species of salamanders live in North America. Most terrestrial salamanders live in moist forest-floor with litter. They produce aquatic larvae. A number of families live in caves. These caves have constant temperature and moisture conditions. It is an ideal environment for salamander. Salamanders have two families:
1. Plethodontidae: They are fully terrestrial salamander. They lay their eggs on land. Their voting are similar to the adult.
2. Salamandridac: They are commonly called newts. They spend most of their lives in water. They retain caudal fins.
The length of salamanders is from a few centimeters to 1.5 m. The largest North American salamander is the hellbender (Crysobranchus alleganiensis). Its lengths reach up to 65c m.
Fertilization: Most salamanders have internal fertilization. Males produce a pyramidal, gelatinous spermatophore. Spermatophore has a cape of sperms. It deposits spermatophore on the substrate. Females pick up the sperm cap with the cloaca. It stores the sperm in a special pouch called spermatheca.
Development: Eggs are fertilized as they pass through the cloaca. They are deposited singly or in clumps or in strings. Larvae are similar to adults but smaller. Larvae possess external gills a tail fin larval dentition and a rudimentary tongue. The aquatic larva undergoes metamorphoses and forms a terrestrial adult. Many other salamanders undergo incomplete metamorphosis. They are paedomorphic. A phenomenon in which larva ecome sexually mature while still showing larval characteristics is called paedomorphosis.
ORDER GYMNOPHIONA (gymnon, naked + ophineos, like a snake)
1. They have elongate body.
2. They are limbless.
3. They are segmented by annular grooves.
4. They are specialized for burrowing.
5. Their tail is short and pointed.
6. They have rudimentary left lung.
7. They have about 160 species.
Example: Members of the order Gymnophiona are the caecilians.
They live in tropical regions. Caecilians are wormrilike burrowers. They feed on worms and other invertebrates in the soil. Folds in the skin separate the muscle bundles. Therefore, the caecilians appear segmented. A retract le tentacle is present between their eyes nd nostrils. It transpoi ts chemicals from he environment into the olfactory the roof of the mouth. Skin covers the eyes. Thus caecilians are nearly blind.
Fertilization is internal in caecilians. Larval stages are passed within the oviducts. Larva stages the inner lining of the oviducts with fetal teeth for feeding. The young come out from the female. It is similar to adults. Other caecilians lay eggs. These eggs develop into aquatic larvae or embryos. Embryos develop on land.
ORDER ANURA (SALIENTIA) (a, without + oura, tail)
1. Anurans live in most moist environments. A few even occur in very dry deserts.
2. They are tailless amphibians.
3. The limbs are modified tor jumping and swimming. Hind limbs are long and muscular and end in webbed feet.
4. They have five to nine presacral vertebrae with transverse processes.
5. The postsacral vertebrae are fused into a rod like urostyle.
6. Tympanum and larynx are well developed.
7. They have about 3.500 species of frogs and toads.
Example: Frogs, Toads.
Life Cycle of Anurans
Anurans have diverse life histories. Fertilization is external. The eggs and larvae are aquatic. Their larva is called tadpoles. It has well-developed tail. Larval bodies lack limbs. Larva develops limbs near the end of their larval stages. The larvae are herbivores. They possess a proteinaceous beak like structure. It is used in feeding. Anuran larvae undergo rapid metamorphosis and adult body is formed.There are not many differences between toad and frogs, Toads have dry and warty skin. They are mostly live on land. True toads belong to the family Bufonidae.
Difference between Frog and Toad
||They have large sizes.
||They have small sizes.
||They spend most of their life in water or near water.
||They spend most of their life on land.
||They have longer hind legs.
||All their eggs are equal in size.
||Their skin is transparent and less warty.
||They have dry and warty skin.