arthropods

• An Arthropod is an invertebrate with an exoskeleton, a segmented body and paired jointed appendages. 
• Trilobites are an extinct group of marine arthropods. 
• Glabella is linked to buoyancy. 
• Genal spines are used for support on soft sediment. 
• Compound eyes are made up of hundreds of lenses. 
• Pleuron is a one jointed unit of the thorax where legs were attached. 
• Trilobites had an exoskeleton made of calcium phosphate and calcium carbonate. As it grew it moulted its exoskeleton by breaking along the facial suture. 
• They appeared in the Cambrian period and are the most important zone fossil for this time. They achieved peak diversity in the late Cambrian and early Ordovician. There was a reduction in diversity through the late Ordovician and Silurian. They became extinct at the end of the Permian. 
• Nektonic trilobites have a lightweight exoskeleton, streamlined shape, eyes at the front of cephalon and a large glabella filled with fat or oil.