what is invertebrate

An invertebrate is an animal that lacks a vertebral column or backbone, in contrast to the cartilaginous or bony vertebrates. Invertebrates are the most diverse and numerous group of animals on Earth, with more than 90 percent of all living animal species being invertebrates. They range in size from microscopic mites and almost invisible flies to giant squid with soccer-ball-size eyes. Invertebrates can live on land, like insects, spiders, and worms, or in water, like crustaceans, mollusks, and coral. Some examples of invertebrates include sea stars, sea urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails, clams, and squid. Insects are the largest group of invertebrates and have six legs, two antennae, and three body parts. Invertebrates are especially important as agricultural pests, parasites, or agents for the transmission of parasitic infections to humans and other vertebrates. They also serve as food for humans, are key elements in food chains that support birds, fish, and many other vertebrate species, and play important roles in plant pollination.