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.
Most arthropod species are insects. "Insects are the most diverse organisms in the history of life".[1]
Most arthropods live on land. The phylumArthropoda is the only phylum of invertebrates that mostly live on land. But crustaceans (crabs, shrimp and their relatives) mostly live in water.
Arthropods are also the first phylum to develop genuine flight.
Description
Arthropods have a hard exoskeleton. The exoskeleton reduces the loss of water (desiccation). This helps them to live on land without drying out.
Classification
Arthropods are made up of four groups of living animals and one group of extinct animals:
Hexapods include insects and a few other organisms. Hexapods have six legs.
Trilobites are a group of extinct arthropods. Trilobites all lived in oceans. They 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.
