Crustaceans, or shellfish, live in water, with few exceptions, such as the wood louse. Their skeleton is their skin, and this is why it is called an exoskeleton. The exoskeleton is not made of bone but rather of chitin. The most well-known representatives of crustaceans are lobsters, crabs, and shrimps. Most of them live in water, with the exception of land snails.
Insects are small six-legged animals with well over a million different species represented.
Insects are the most adaptable of all animals and we find them on land, in water and flying through the air. Many other animals belong to other less known categories that have not been mentioned here. For example, spiders and scorpions are arachnids, sea urchins and sea stars are echinoderms, jellyfish and anemones are cnidarians, andthe thousands of sorts of worms and sponges come from many more different classes. As you can see, the animals kingdom is incredibly numerous and varied.