Published on Dec 20, 2019

Crab Background Images

License Info: Creative Commons 4.0 BY-NC

We all are familiar with them. They are very much relished as food. Sometimes they look dangerous because of their appearance and we get frightened. They are crabs. Crabs are the decapods crustaceans belonging to the infraorder Brachyura. They are demarcated by reduced abdomen which is generally hidden beneath the cepahalohoax.

Some animals like the hermit crab, king crab and the porcelain crabs are not true crabs. The body crabs is covered by a thick exoskeleton and are provided with only one pair of claws known as chelae. They inhabit all the marine oceans of the world. Few species are also found in the freshwaters and few on land specially those belonging to the tropical regions. Pea crab is the smallest crab known measuring only few millimeters in length. The Japanese spider crab has been known to have a leg span on 4 meters and is the largest crab known ever.

About 850 species of crab are known to dwell in the tropical and semi-tropical regions and are freshwater, terrestrial or semi-terrestrial. Earlier it was believed that they belonged to a same monophyletic group but now it is clear that they are the members of two different lineages, the Old World and the New World.


The earliest fossils of crab have been recorded from the Jurassic period and are in the form of the carapace. They flourished in different parts of the world during the Cretaceous period. They are also known to exhibit sexual dimorphism. Males have larger claws and this feature is very much pronounced in fiddler crabs of the genus Uca. In the fiddler crabs one of the claws of male is larger and is particularly used for communication specially for attracting the mate. Another difference between male and female is that the males have a narrow and triangular abdomen while the females have a broader and rounded abdomen. This is because the female crabs brood their fertilized eggs on the pleopods.

The articulation of the legs is responsible for the sideways movement. Some species are able to move forwards and backwards also and some are also adapted for swimming. Crabs are very active animals and show complex behavioural patterns. They are also known to communicate by waving their pincers. A tough fight has been observed among the males for females especially during courtship.

Crabs are seen fighting over the holes on the seashores. They are omnivorous and are known to feed upon molluscs, algae, worms, and detritus depending upon the availability of food. It has been observed that if a crab feeds on a mixed diet of plants and animals it develops faster. Crabs are known to work in a team and guard the family very well. During the mating season female is well protected by the family members so that the fertilized eggs may get full chance to survive and result in a fruitful progeny.

Crabs form 20% of the sea food caught from the oceans and exported worldwide. They are cooked in a variety of ways and are very much relished as food. Live crabs are boiled and form a very popular delicacy in Norway.

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