A crab is a decapod crustacean with a broad carapace, stalked eyes, a short projecting tail and five pairs of legs. The first pair serves as pincers which have functions of defend, communicating and picking up things. It has a thick exoskeleton that supports and protects its body. Crabs usually tend to walk sideways, the name crabwise is given to their specific style. They may also adopt different style like walking backward or forward. Many crabs are capable of swimming. Crabs are found all over the world, mostly in tropical areas, in fresh water, ocean water and on shores. Naturally, crabs are marine animals, however they become adapted to life on land. There are about 850 species of crabs. Other marine animals like horseshoes crab, crab lice, king crabs, hermit crabs, porcelain crab share their name but are not really crabs. Crabs show profound sexual dimorphism. Different crabs diseases may also affect them. Crabs diseases can be caused by Vibrio bacteria, Rhodo bacteria, viruses, parasites, protozoans and several other pathogenic organisms.
Crabs are quite complex and competitive animals. They communicate through their pincers or by drumming. Males crab are hostile towards each other and fight over mating partners, prey and home (hiding holes). However, crabs also tend to be social and work in groups to gain food and protect each other. During mating seasons, they look for a place where females can lay their eggs. They are omnivores and eat whatever is available for instance, plants, fungi, other crustaceans, algae, molluscs, bacteria, detritus and worms. Studies have shown that a balanced diet consisting of both plants and meat result in greater health and physical fitness.
There are many crabs diseases out there. Pepper spot disease of crab is caused by a parasite, usually a flatworm or fluke, that in turn becomes infected with another parasite (by a protozoa named Urosporidium crescens). The term Hyperparasite is used for the secondary parasite. Clinically, it can be seen as black flecks and spots on the crab. Only aesthetic of crabs are affected otherwise the crab meat is safe, although many people are apprehensive to eat. Another common disease is Bitter Crabs diseases. It is caused by a Dino flagellate that exclusively feeds on crab's blood. The oxygen from the blood is consumed causing clotting disorders. The crabs become severely weak and ultimately die. The infection occurs in outbreak and the shores my be full of dead or lethargic crabs. The disease is called bitter because when the infected crabs are cook they give an awfully bitter taste. Cotton or cooked crabs diseases are uncommon and caused by a microsporodium, Ameson Michaelis. It is a degenerative disease that destroys crab's muscles. Shell disease is a chitinivorous bacterial disease that result in burn 'brown' spots on crabs' shells. Rhabdovirus causes a neurological disease while Reolike virus causes a hemopoetic disease. Other crabs diseases are caused by herpes virus, fungi, protozoa and helminths.
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Crabs have several cultural influences like astrological sign and constellation sign Cancer. The word cancer for malignancy is also derived from crab. Crabs are largely consumed all over the world and there are millions of crab fisheries. Some of the crab dishes are Bisque, black pepper crab, crab cake, Chilli crab, Bun reiu, Deviled crab, crab Rangoon, crab dips and seasonings and countless more.