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Vertebrates
Vertebrates (Vertebrata) are a group of chordates that includes about 57,000 living species. Members of this group include lampreys, mammals, birds, amphibians, reptiles, and fishes. Vertebrates have a vertebral column in which the notochord is replaced by multiple vertebrae that form a backbone. The vertebrae surround and protect a nerve cord and provide structural support.
| Chordates
Chordates (Chordata) are a group of animals that includes more than 75,000 living species. Chordates are divided into three basic groups: vertebrates, tunicates, lancelets. Of these, the vertebrates—lampreys, mammals, birds, amphibians, reptiles and fishes—are the most familiar and are the group to which humans belong.
| Animals
Animals (Metazoa) are a group of living organisms that include more than one million identified species and many millions more that have yet to be named. Scientists estimate that the number of all animal species—those that have been named and those that have yet to be discovered—lies somewhere between 3 and 30 million species.
| Segmented Worms
Segmented worms (Annelida) are a group of invertebrates that includes about 12,000 species of earthworms, ragworms and leeches. Segmented worms live in marine habitats such as the intertidal zone and near hydrothermal vents. Segmented worms also inhabit freswater aquatic habitats as well as moist terrestrial habitats such as forest floors.
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