Introduction to Amphibia:
The Amphibians made initial transition from aquatic to terrestrial mode of life; they were first to venture out of water and live on land. Examples of amphibians comprise toads, frogs, Newts and Salamanders. Many of them live in moist environments and return to water to breed.
Features of Amphibians:
The features of amphibian are given below:
i) It is cold-blooded.
ii) It has paired fore-and hind limbs in adult stage.
iii) It contains a naked, moist skin.
iv) It contains the sticky tongue that can be protruded and retracted quickly.
v) It contains inner and middle ears.
vi) It performs gaseous exchange by lungs, gills, skin or mouth lining, individually or in combination. Gills are present at some stage in the life cycle.
vii) It contains the three-chambered heart.
viii) Fertilization is external. Eggs are small.
ix) The aquatic larval stage is generally present.
External Features of the Toad and Frog:
Toads are awkwardly built creatures, generally 10cm long but sometimes growing to larger size. They contain brown, wrinkled and warty skin with darker spots and markings on upper surface and white undersurface. There are swellings such as rough warts over eyes. Legs are shorter than frogs; hind legs being little longer than body. They do not have teeth. Tongue, that is attached in front of mouth but is free behind, is only somewhat cleft at tip but still it is insectcatching apparatus of great perfection. Male toad is smaller than female. Toads are terrestrial and nocturnal in habit. In day time they usually lie covered under stones or in other damp and shady places and come out only towards evening.
Ecological Adaptation of Amphibians:
Amphibians are as class, characteristically furnished with 5 fingered limbs that are adapted for locomotion both on land and in water. They are cold -blooded or poikilothermic animals of jumping and swimming habits. Skin is clammy, smooth and naked, which is without scales. There is amazing difference between young and adults; limbless but tailed young forms or tadpoles, as they are called, dwell in water and breathe by gills whereas almost in all case adults breathe by lungs and live both on land and in water and thus name amphibian. Skin is generally soft and moist to carry on significant functions of skin or cutaneous respiration and this is reason why presence of moisture is necessary for well being of amphibians.
Tailless amphibians, like frogs and toads, numbering some thousand species, have worldwide distribution. They are most in abundance located in tropical countries. Bu it is amazing that despite their natural preference to live in and around water no amphibian has found to live in salt and marine waters.
Difference between Frog and Toad:
It is mainly aquatic
It lives on land among stones in damp places.
It is diurnal in habit, that is, it comes out mainly during the day time.
It is mainly nocturnal.
It does not possess good sense of locality.
As it has a good sense it can keep within a certain locality for a long time.
It shows quick and nervous movement.
It shows sluggish creeping movements, which seem to be carried on with greater sense of security.
The skin is smooth and slippery.
The skin is always rough, nearly dry, wrinkled and warty.
Skin is provided with relatively few poison glands.
Skin is abundantly supplied with poison glands and irregularities of the skin are mainly caused by the large number of poison glands contained in them.
Outline of Adaptive Features:
Skin secretes substances which fright away enemies (other animals) like Snakes from attack. Tongue is the insect-catching apparatus that helps feeding. It has five fingered limbs for locomotion. It has webbed feet for swimming and strong hind -legs for jumping/leaping. Soft moist skin or cutaneous for respiration. Young ones, Tadpoles dwell in water and breathe by gills. Tadpoles contain the streamline body. Tadpole has fin-like tail which helps swimming. Adults breathe by lungs thus can live in land and water.
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