Crustacean is a term that indicates a class of aquatic Arthropoda with a body divided into cephalothorax (head and thoracic segments) and abdomen (divided into several segments).
The crustaceans are provided with a hard shell articulated by joints that allow them to move. They can be divided into three groups: the "Macruri" with an elongated abdomen - called tail - ending in a fan-shaped fin; lobsters, prawns and shrimps belong to this category.
The second group is constituted by the «Brachiuri» with short, broad abdomen equipped with large pincers; the crab and spider crab belong to this family. Finally, the third category is the "Stomatopoda" which includes only the family of the Squillids, namely the mantis shrimp, whose front legs are extensions of its mouth. The shell of some crustaceans undergoes a change of color with cooking.