Their earliest order is Redlichiida, which did not have the natant hypostome of the ensuing Ptychopariida and Harpetida types, and the Proetida were the longest-lasting.  
These organisms may have evolved from Spriggina and Parvancorina, while those of the order Lichida may have had horns. Their earliest order is Redlichiida, which did not have the natant hypostome of the ensuing Ptychopariida and Harpetida types, and the Proetida were the longest-lasting.  Though the Agnostina were eyeless, other orders were among the first species to develop complex compound eyes.  Containing over 17,000 identified species, they came into existence during the Cambrian period but died off with most other marine species during the Permian-Triassic Extinction.  For 10 points, name these small arthropod fossils, named for their three-lobe structures.
These organisms may have evolved from Spriggina and Parvancorina, while those of the order Lichida may have had horns.
trilobites