Crabs The Armoured Para-Aquatic Creture-Facts

The crab is one of the oldest species on earth. The horseshoe crab dates back over 200 million years and is literally a living fossil. It is omnivorous in nature and feeds on a diet comprising of algae, mollusks, worms, other crustaceans, fungi, bacteria and detritus, etc. Crabs and other crustaceans can feel and remember pain, contrary to popular belief. The teeth of a crab are in its stomach. The biggest crab till date was found in Maryland. It was a male and measured 9 inches. Crabs are generally covered with a thick exoskeleton, composed primarily of calcium carbonate, and armed with a single pair of chelae (claws). Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres (13 ft). Crabs often show marked sexual dimorphism. Males often have larger claws. Crabs typically walk sideways(a behaviour which gives us the word crabwise). This is because of the articulation of the legs which makes a sidelong gait more efficient. However, some crabs walk forwards or backwards, including raninids, Libinia emarginata and Mictyris platycheles. They can communicate by drumming or waving their Claws.  Crabs tend to be aggressive towards one another and males often fight to gain access to females. Female blue crabs mate only once in their lives. Crabs are known to work together to provide food and protection for their family, and during mating season to find a comfortable spot for the female to release her eggs. Crabs make up 20% of all marine crustaceans caught, farmed, and consumed worldwide, amounting to 1½ million tonnes annually. One species, Portunus trituberculatus, accounts for one fifth of that total. Crabs are prepared and eaten as a dish in several different ways all over the world. The biggest importers, and therefore countries where eating crab is immensely popular, are Japan, France, Spain, Hong Kong, the US, Canada and Portugal. The blue crab is so named because of its sapphire-tinted claws. Its shell, or carapace, is actually a mottled brownish color, and mature females have red highlights on the tips of their pincers. Blue crabs are extremely sensitive to environmental and habitat changes, and many populations, particularly in the Chesapeake Bay in the eastern United States, have experienced severe declines. Crabs actually have ten appendages (legs). Therefore they are known as decapods (deca = ten, poda = leg). Out of these, the first pair of appendages are modified into claws, which are biologically known as chelae. The male crabs have narrow abdomens, while the female crabs have broader abdomens. Japanese Spider Crab can have a walking leg span of 3 to 4 m, which can go to 8 m when outstretched. The most colorful crab in the world is probably the Sally Lightfoot Crab. It has red, orange, yellow and white colors.