Invertebrates are not distinguished by a single positive characteristic. Instead, they are defined by the fact they do not have a backbone, or any bones at all for that matter. They also have no cartilidge. Invertebrates make up more than 95% of all known animal life, encompassing numerous species such as jellyfish, sponges, coral, insects, worms, arachnids, crabs, squids and many, many more.