Subphylum Trilobitomorpha involves the trilobites. All species are extinct and the fossils point out that they were all marine forms belonging to Paleozoic era. They are the most primitive of all arthropods. Body was categorized into three lobes by means of two furrows longitudinally; distinct head, thorax and abdomen were present. Appendages biramous it appears that trilobites had a range of habits; they included epibenthic, crawling, burrowing, planktonic and swimming forms.