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, and they are distributed into more than 30 phyla. They can be found practically anywhere and provide many services that are vital for our survival. Invertebrates can be classified into various groups, including insects, arachnids, crustaceans, mollusks, and worms. Some examples of invertebrates include sea stars, sea urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails, clams, and squid.

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 and are key elements in food chains that support birds, fish, and many other vertebrate species. Invertebrates play important roles in plant pollination, and without them, many plants would not be able to reproduce, and humans would lose access to many essential food sources.

In summary, an invertebrate is an animal without a backbone, and they are the most diverse and numerous group of animals on Earth. They can be found practically anywhere and provide many services that are vital for our survival.