An animal that does not have a backbone is called an invertebrate. Invertebrates make up 95% of all animal species and include a wide variety of organisms such as insects, mollusks, and jellyfish. Unlike vertebrates, which have spinal columns, invertebrates have different structural adaptations for support, movement, and protection. The diversity of invertebrates is immense, and they play critical roles in ecosystems, such as pollinators, decomposers, and a primary food source for many vertebrate animals.