Invertebrates are all species of animals without a backbone or spine, which includes arthropods (insects, crustaceans, etc.), mollusks (bivalves, snails, squid, and octopus, etc.), annelids (worms, etc.), and cnidarians (corals, anemones, jellyfish, etc.). The earliest fossils appear to be invertebrates which have been dated back to 665 million years ago. Invertebrates are the largest class of animals, comprising 97% of the animal kingdom with 1.25 million species discovered, but millions still to be discovered. A key to the large quantity of invertebrates is their ability to reproduce quickly and abundantly, with some species’ members producing both egg and sperm, and some species laying eggs that do not require fertilization. Invertebrates are comprised of a wide range of species, all the way from microscopic mites to the giant squid.
Invertebrates can effectively protect their soft bodies through an outer hard casing that is referred to as the exoskeleton. Invertebrates like spiders, crustaceans, and insects have their exoskeletons made through sections of jointed legs. Others like mollusks like snails and clams have a hard shell in which they can hide when danger is present.
The difference between an invertebrate and a vertebrate is that invertebrates have no backbones while vertebrates have a developed internal skeleton with cartilage and bones as well as a developed brain that is protected by a skull. Vertebrates also cannot make their food, while invertebrates make their food.
Invertebrates are important because like bees they help with pollination, as well as help clear and clean up the environment. Invertebrates are also important because they are soil aerators and creators as they help grow food crops. They also provide eco-system balance and serve as food for other species within the food chain.