Monday, 8 August 2011
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" or where the reduced abdomen is entirely hidden under the thorax. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs and crab lice – are not true crabs.Crabs are generally covered with a thick exoskeleton (shell), and armed with a single pair of chelae (claws). Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land, particularly in tropical regions.
About 850 species of crab are freshwater, terrestrial or semi-terrestrial species; they are found throughout the world's tropical and semi-tropical regions. They were previously thought to be a monophyletic group (group of organisms).Crabs often show marked sexual dimorphism. Males often have larger claws,a tendency which is particularly pronounced in the fiddler crabs of the genus Uca (Ocypodidae).
In fiddler crabs, males have one claw which is greatly enlarged and which is used for communication, particularly for attracting a mate. Another conspicuous difference is the form of the pleon (abdomen); in most male crabs, this is narrow and triangular in form, while females have a broader, rounded abdomen. This is due to the fact that female crabs brood fertilised eggs on their pleopods.
King crabs, also called stone crabs, are a subfamily of crab-like decapod crustaceans chiefly found in cold seas. Because of their large size and the taste of their meat, many species are widely caught and sold as food, the most common being the red king crab, Paralithodes camtschaticus.
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.
Prized by humans for their sweet, tender meat, these wide-ranging, ten-legged crustaceans are among the most heavily harvested creatures on the planet. Their scientific name, Callinectes sapidus, means "savory beautiful swimmer." Blue crabs are extremely sensitive to environmental and habitat changes,Blue crabs also play a key role in managing the populations of the animals they prey on, and constant overharvesting has had wide-ranging negative effects on the ecosystems they inhabit.
Chionoecetes is a genus of crabs that live in the northern Pacific and Atlantic Oceans.Other names for crabs in this genus include "queen crab" and "spider crab" - they are known by different names in different areas of the world. The generic name Chionoecetes means snow (snow crab).