Invertebrates make up 95% of all animal species and do not have backbones. They are classified into eight categories: sponges, which have no symmetry; cnidarians like jellyfish that have stinging tentacles; mollusks such as clams and oysters that all have shells; echinoderms with spiny skin and internal skeletons; arthropods including insects, spiders, crabs, and centipedes with hard exoskeletons; and three types of worms - flatworms, roundworms, and segmented worms that live inside and on land and sea animals.