1. 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

2. 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

3. Class Trilobita
Extinct arthropods --important part of the early fossil record

4. Trilobites
First appear at the base of the Cambrian approximately 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

5. Trilobite Environments
Exclusively marine
Common in shallow sea deposits of Cambrian and Ordovician

6. 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
© by S. M. Gon

7. Ventral View
Dorsal View.

8. 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

9. 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