Arthropod Exoskeleton: Evolving to occupy land
This exoskeleton may work to advantage for animals to colonize land if a mechanism of breathing in air as opposed to water can be secured. By developing almost closed air chambers lined with folds of moist skin crustaceans are able to absorb oxygen from air. In this way sand shrimps, beach hoppers and wood lice have been able to colonize land that retains a moist environment. The most spectacular of land dwelling crustacean is the big robber crab Birgus which exploits coconuts.
Other descendent of the invertebrates have left the sea for a terrestrial life style the first of which were probably derived from segmented marine worms, but more recently included the familiar snails and slugs. These changes started about 400 million years ago and gave rise to the most numerous and diverse of land animals; the insects.