Description
shellfish are a class of arthropod animals, generally aquatic, with a body made up of segments covered with a chitinous shell. This class includes animals such as shrimp, krill, isopods, crabs, crayfish and others. These animals appeared in the Cambrian period, about 511 million years ago, and are still alive today. The body of a crustacean is made up of segments, which are grouped into three regions: head, cephalothorax and an abdomen, protected or not by a shell, being covered with a crust of limestone and chitin. Crustaceans breathe through the entire surface of the body or through gills and their blood is blue due to a pigment.
Crustaceans range in size from 0.1 mm (Stygotantulus stocki) to 3.8 meters (the Japanese spider crab) and may feed on algae, plankton, snails, plants, or the eggs of other animals. Most crustaceans are free-living aquatic animals, but some are terrestrial (e.g., woodlice), and some are parasitic.




























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