The Phylum Arthropoda is probably the most diverse and widespread group of animals on Earth.
Arthropods are abundant in terrestrial, marine, and freshwater aquatic habitats.
Their success is probably related to some of the main features of their body plan, which we will explore in detail below. There are four main groups of arthropods. They have mandibles for feeding and they have biramous appendages . They have piercing mouthparts called chelicerae for feeding and book gills or book lungs for respiration. They have many segments with fairly undifferentiated legs and they use their tracheal system for respiration.