The arthropods are by far the most successful phylum of animals, both in diversity of distribution and in numbers of species and individuals. They have adapted successfully to life in water, on land and in the air.
80% of all known animal species belong to the Arthropoda - about 800,000 species have been described, and recent estimates put the total number of species in the phylum at about 6 million.
Arthropods are found in a greater variety of habitats than any other animal group; on top of mountains, at great depths in the ocean and in the icy wilderness of Antarctica. They can survive great extremes of temperature, toxicity, acidity and salinity.
Now extinct, trilobites represent the oldest known examples of arthropods.
An extremely diverse phylum with many classes both large and small, there are several classifications of the phylum.