Applied Science, Life Science, Biology
Material Type:
Community College / Lower Division, College / Upper Division
Rice University
Ambulacral System, Annelid, Annelid Anatomy, Annelid Morphology, Annelida, Anthozoa, Archenteron, Arthropod, Arthropod Morphology, Arthropoda, Biramous Appendage, C. Elegans, Captacula, Cephalothorax, Chaetae, Chelicerata, Clitellum, Cnidaria, Cnidarian, Cnidocyte, Coelenteron, Coelom, Coelomate, Conspiral, Crustacea, Ctenidia, Cubozoa, Cypris, Echinoderm, Echinoderm Anatomy, Echinoderm Excretory System, Echinoderm Morphology, Echinoderm Nervous System, Echinoderm Reproduction, Echinodermata, Enterocoelous Coelom, Eucoelomate, Gemmule, Hemocoel, Hermaphrodite, Hexapoda, Hydrozoa, Invertebrata, Invertebrate, Lophotrochozoa, Madreporite, Mantle, Medusa, Mesoglea, Mesohyl, Metamerism, Mollusca, Myriapoda, Nacre, Nauplius, Nematocyst, Nematoda, Nematode, Nematode Excretory System, Nematode Morphology, Nematode Nervous System, Nematode Reproduction, Nemertea, Nemertea Digestive System, Nemertea Morphology, Nemertea Nervous System, Nemertea Reproduction, Osculum, Ostia, Oviger, Pedipalp, Phylum Annelida, Phylum Arthropoda, Phylum Cnidaria, Phylum Echinodermata, Phylum Mollusca, Phylum Nematoda, Phylum Nemertea, Phylum Porifera, Pilidium, Planospiral, Planuliform, Polyp, Porifera, Pseudocoelomate, Radula, Rhynchocoel, Schizocoelous Coelom, Sclerocyte, Scyphozoa, Sponge, Sponge Locomotion, Sponge Metabolism, Sponge Morphology, Sponge Reproduction, Spongocoel, Superphylum Lophotrochozoa, Trocophore, Uniramous Appendage, Veliger, Zoea
Creative Commons Attribution-NonCommercial 4.0


Section 1

The photo shows a purple and orange starfish on a sandy flat beach.
Nearly 97 percent of animal species are invertebrates, including this sea star (Astropecten articulates) common to the eastern and southern coasts of the United States (credit: modification of work by Mark Walz)

A brief look at any magazine pertaining to our natural world, such as National Geographic, would show a rich variety of vertebrates, especially mammals and birds. To most people, these are the animals that attract our attention. Concentrating on vertebrates, however, gives us a rather biased and limited view of biodiversity, because it ignores nearly 97 percent of the animal kingdom, namely the invertebrates. Invertebrate animals are those without a cranium and defined vertebral column or spine. In addition to lacking a spine, most invertebrates also lack an endoskeleton. A large number of invertebrates are aquatic animals, and scientific research suggests that many of the world’s species are aquatic invertebrates that have not yet been documented.