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Arthropods (Greek language for "joint-legged") are a large group of invertebrate animals. Insects, spiders, crabs, shrimp, millipedes, and centipedes are all arthropods. In the scientific classification, all arthropods are members of the phylum Arthropoda. Arthropods have segmented body, an exoskeleton and legs with joints. Most arthropods live on land, but some live in water. Arthropods have by far the greatest number of species of any animal group. Arthropods are a source of food for many animals, including humans.
Scientists know of more than 1 million species of arthropods. 80% of all known animal species are arthropods. Many more species have not yet been described.
Arthropods are also the first phylum to develop genuine flight.
Arthropods are made up of four groups of living animals and one group of extinct animals:
- Chelicerates include horseshoe crabs, spiders, mites, and scorpions.
- Myriapods include millipedes and centipedes.
- Crustaceans include lobsters, crabs, barnacles, crayfish and shrimp. Most crustaceans live in water.
- Hexapods include insects and a few other organisms. Hexapods have six legs.
- Trilobites are a group of extinct arthropods. Trilobites all lived in oceans. Trilobites disappeared in the Permian–Triassic extinction event, about 252 million years ago. The trilobites are the second most famous type of fossils, after the dinosaurs.