Phylum Arthropoda Arthropoda is largest phylum in animal kingdom Arthropoda consists of about 700,000 species or about three fourths of all known kinds of animals Consists of spiders, crustaceans (crabs, lobsters, shrimp, ostracods, etc.), insects, centipedes, and the extinct trilobites Arthropod means “jointed foot” Arthropods have been around for approximately 550 million years
Arthropods Continued Arthropods have a segmented body that is bilaterally symmetrical External covering composed of chitin Develop from an egg and then pass through a larval stage
Class Trilobita Extinct arthropods --important part of the early fossil record
Trilobites First appear at the base of the Cambrian approximately 530-525 m.y. ago Reach their maximum in late Cambrian early mid-Ordovician Trilobites declined during the Silurian and Devonian Rare in the Pennsylvanian Disappeared end of Permian (about 250 m.y ago) Trilobites found at base of the Cambrian structurally complex, suggesting evolution from earlier ancestor
Trilobite Environments Exclusively marine Common in shallow sea deposits of Cambrian and Ordovician
Trilobite Morphology The trilobite body divided into three areas: the Cephalon, the Thorax, and the Pygidium. Trilobite means “three lobed” -- named for axial lobe and two pleural lobes ©1999 - 2007 by S. M. Gon http://www.trilobites.info/trilobite.htm
Ventral View Dorsal View. http://www.trilobites.info/trilomorph.htm
Horsehoe crab Chelicerate arthropod—Orodovician to present. Differ from other arthropods—no antenne More closely related to spiders, ticks, and scorpions than to true crabs Wikipedia
Giant Isopod A giant isopod may be one of approximately nine species of large isopods (crustaceans related to the shrimps and crabs) in the genus Bathynomus. They are thought to be abundant in cold, deep waters of the Atlantic and Pacific Ocean. Bathynomus giganteus, the species upon which the generitype is based, is the largest known isopod and is the one most often referred to by the common name "giant isopod". Wikipedia