characteristics of frog and crab~

        A frog is an amphibious animal. They belong to the order Anura.
Frogs can live on land and in fresh water. Frogs cannot survive in salt water. They hatch as tadpoles from eggs, which are laid by a female frog. The eggs are called frogspawn. Tadpoles have tails and gills. When they grow up, they lose their tails and gills and grow four long legs. Grown frogs can jump far with their legs. They have long tongues that they use to catch bugs. They make a sound called a croak. They sometimes live in tree, and some types of frog are capable of making poison. Frogs live all over the world, apart from Australia. Different types of frogs are native to different countries and have different characteristics that relate to the environment of this country. If an overseas species of frogs is introduced to another country, the ecosystem can be hugely affected.
Frog legs are occasionally eaten as food in France, China, and the Midwest of the United States. The killing of frogs has an effect on the ecosystem. For example, frogs eat mosquitoes. If frogs are killed, then there are less frogs to eat mosquitoes, so more and more mosquitoes are born. Therefore, in these areas, there are more diseases that mosquitoes carry, because there are more mosquitoes.
        Frogs have very good eyesight. They bulge out the sides of their heads in order for the frog to see in nearly all directions.  
Frogs also have amazing sense of hearing. You can often tell the difference between a male and female frog by the size of their eardrum, which can be seen behind their eyes. If the eardrum is smaller than the eye, the frog is a female. On males their eardrum is the same size as the eye.
Frogs have very powerful back legs and webbed feet that help them jump great distances, as well as, swim. Frogs even use their legs to dig, or burrow, underground for hibernating. Certain frogs can jump up to 20 times their own body length in a single leap. 

Every different species of frog has his or her own look. They come in many colors, patterns and sizes.


        Frogs need to live near water,have smooth,moist skin that makes them look “slimy”, have a narrow body, have higher,rounder,bulgier eyes, have longer hind leg, take long high jumps, and have many predators.

CRAB


Crabs are in the phylum Crustacea. They are decapods (ten legs), along with lobsters, crayfish and shrimps. Crabs form an order within the decapods, called the Brachyura. Their short body is covered by a thick exoskeleton.
They are an extremely successful group, found all over the world. They are basically heavily armoured shell-breakers. Most crabs live in sea-water, but there are some who live in fresh water, and some who live on land. The smallest are the size of a pea; the largest (the Japanese Spider Crab) grows to a leg span of 4 metres. About 7,000 species are known.

Structure and life-style

 Body

Crabs have very short tails. A crab's tail and reduced abdomen is entirely hidden under the thorax. It is folded under its body, and may not be visible at all unless you turn the crab over. Usually they have a very hard exoskeleton. This means they are well protected against predators. Crabs are armed with a single pair of claws. Crabs can be found in all the oceans. Some crabs also live in fresh water, or live completely on land.

Pincers

The pincers (claws) of crabs are their most important weapons. They have at least three functions. The pincers' role in eating is to seize and subdue the prey. If the food is a shellfish (mollusc), then the pincers can exert force to open or break the mollusc's shell. Pincers are also used in fighting between males, and for signalling to other crabs.

Food

Crabs are omnivores, they eat almost anything they find. Often this is algae, but animal food is essential for its good health and development. They will eat molluscs, other crustaceans, worms, fungi and bacteria.

Crabs as food

Crabs are prepared and eaten all over the world. Some species are eaten whole, including the shell, such as soft-shell crab; with other species just the claws and/or legs are eaten. In some regions spices improve the culinary experience. In Asia, Masala Crab and Chilli crab are examples of heavily spiced dishes. In Maryland, blue crab is often eaten with Old Bay Seasoning.
For the British dish Cromer crab, the meat is extracted and placed inside the hard shell. One American way to prepare crab meat is by extracting it and adding a flour mix, creating a crab cake. Crabs are also used in bisque, a French soup.

Evolution

True crabs appear in the fossil record in the Lower Jurassic. They are part of the 'Mesozoic marine revolution', in which a number of sea-floor predators evolved.

 Tailpiece

The closest relatives of the crabs are anomurans, a crustacean group which includes animals such as hermit crabs, king crabs and squat lobsters. They look a lot like crabs and many have the word 'crab' in their name, but are not true crabs. Anomurans can be told apart by the number of legs: crabs have ten legs, including claws, while the last pair of an anomuran's legs is hidden inside the shell, so that only eight legs are visible.