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The decapod (crustaceans, such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon . [1] [2] Each segment may possess one pair of appendages, although in various groups these may be reduced or missing. They are, from head to tail:
At the time of moulting, the crab takes in a lot of water to expand and crack open the old shell at a line of weakness along the back edge of the carapace. The crab must then extract all of itself – including its legs, mouthparts, eyestalks, and even the lining of the front and back of the digestive tract – from the old shell. This is a ...
A shed carapace of a lady crab, part of the hard exoskeleton Body structure of a typical crustacean – krill. The body of a crustacean is composed of segments, which are grouped into three regions: the cephalon or head, [5] the pereon or thorax, [6] and the pleon or abdomen. [7]
The urchin crab is a brownish-pink colour and grows to a length of about 5 cm (2 in). It has long-stalked eyes, a rounded carapace and long, slender legs. It uses only the first two pairs of legs for locomotion because the third and fourth pairs are used to grip a sea urchin which it carries around on its back.
Classification within the order Decapoda depends on the structure of the gills and legs, and the way in which the larvae develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata. The Dendrobranchiata consist of prawns, including many species colloquially referred to as "shrimp", such as the "white shrimp", Litopenaeus setiferus .
Concerning their walking legs, their first three are compressed; their chelipeds, or pincers, are usually smaller, shorter, or equal to their walking legs. [3] Snow crabs are iridescent and range in color from brown to light red on top and from yellow to white on the bottom, [ 1 ] and are bright white on the sides of their feet.
[25]: 556 If severed from the body, lost legs or the telson may slowly regenerate, and cracks in the body shell can heal. [26] Difference between the pedipalps of male (right) and female (left) horseshoe crabs. Pedipalps are highlighted in grey. The opisthosoma or abdomen of a horseshoe crab is composed of several fused segments.
Dungeness crabs have four pairs of armored legs, two claws, and a wide, hard shell. A Dungeness's legs are shorter compared to other commercial crabs [7] and their claws have a distinctive hook. [3] The claws of the crab are used both as defense and to tear apart large food items.