A group of invertebrate animals consisting of some 45,000 species distributed worldwide. They’re aquatic or amphibic arthropods with hard shell, segmented body and jointed appendages such as crab, lobster, barnacles, shrimp, and copepods. Crustaceans are generally aquatic and differ from other arthropods in having two pairs of appendages (antennules and antennae) in front of the mouth and paired appendages near the mouth that function as jaws. They’re a very important part of Arctic food chain as a part of zooplankton.
Photo: Calanus glacialis, https://earthlingnature.wordpress.com