Invertebrate

Invertebrates are animals that do not possess or develop a vertebral column (commonly known as a backbone or spine), derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include insects, crabs, lobsters and their kin, snails, clams, octopuses and their kin, starfish, sea-urchins and their kin, and worms. The majority of animal species are invertebrates; one estimate puts the figure at 97%.

Characteristics

Invertebrates can be classified into several main categories, some of which are taxonomically obsolescent or debatable, but still used as terms of convenience. They are: Arthropods, Molluscs, Annelids, Nematodes, Platyhelminthes, Cnidaria, Porifera, Echinoderma, and others.

Evolution

The earliest animals were marine invertebrates, among them molluscs and arthropods, both of which have significant numbers of preserved species in the fossil record.

Classification

Invertebrates are often classified by their structure and function. The classification of invertebrates is a subject of ongoing debate.

See also

• List of invertebrates
• Invertebrate zoology
• Invertebrate paleontology

References

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External links

• UCMP: Introduction to the Invertebrates
• UCMP: Systematics of the Metazoa

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