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. They are terrestrial or aquatic, and they also respire with their tracheal system.
Insects are the most diverse group of arthropods.
Several million species have already been described and millions more remain unnamed. Arthropods have colonized terrestrial habitats several times. The chelicerates, the insects, and myriopods have also colonized land. Today we will examine the morphology of a terrestrial insect, the grasshopper, closely. While we are doing so, you should think about the features of this organism that allow it to survive in a terrestrial environment.