Grade 3-4, Life, Invertebrates UnitThe book Invertebrates explains that invertebrates are a large and varied group of animals that lack a backbone. They comprise the majority of the population, variety, and mass in the animal kingdom. Invertebrates share many common features, such as being multicellular, being cold-blooded, and not having lungs. Scientists classify invertebrates into groups of animals with shared characteristics. The book explores several common invertebrate groups. Students will learn about the locomotion, diet, size, body structure, and habitat, as well as other characteristics that make each group of invertebrates unique.