They have triploblastic coelomates with bilateral symmetry
Arthropods have a segmented body, a tough exoskeleton and jointed appendages
They show extensive cephalization with many sensory structures at the anterior end.
They have a open circulatory system.
Structure & Function
Gas exchanges methods (respiratory) Gills in aquatics, tracheal tubes in insects, and book lungs in spiders.
The entire body is covered in an exoskeleton constucted of layers of protein and chitin.
Well-developed sense organs including eyes (sight), olfactory (smell), and tactile receptors (touch) are present at the anterior end.
Open circulatory system containing hemolymph.
How Many Species?
Over 1 Million
Atlantic horseshoe crab
Asian lady beetle
3 Interesting Facts
1. Ancestral arthropods were the first land animals 2. The oldest arthropod known to have lived on land is the Pneumodesmus newmani. 3. The word arthropod is derived from Greek words meaning 'joint' and 'leg'.
Habitat
Arthropods are found in virtually every known marine (ocean-based), freshwater, and terrestrial (land-based) ecosystem, and vary tremendously in their habitats, life histories, and dietary preferences.