Sub phylum Trilobitomorpha were a dominant form of life in the ocean from the Cambrian period (600 million years ago) to the Carboniferous period (345 million years ago).They crawled along the substrate feeding on annelids,molluscan and decaying organic matter.The trilobite body was oval,flattened,and divided into three longitudinal regions.All body segment articulated so that the trilobite could roll into a ball to protect its soft ventral surface.Most fossilized trilobite are found in this position.
Trilobite appendages consisted of two lobes or rami and are called biramous appendages.Their inner lobe was a walking leg ,and outer lobe bore spike or teeth that may have been used in digging or swimming or as gills in gas exchange.