Trilobite Order Harpetida

The most salient and distinguishing trait of the Harpetida (pronounced Har-pe-tee-da) is a semicircular brim surrounding the

Trilobite Taxonomy	Trilobite Phylogeny
Phylum Arthropoda Subphylum Chelicerata or Subphylum Schizoramia * Superclass Arachnomorpha * Class Trilobita Order Agnostida Order Redlichiida Order Corynexochida Order Phacopida Order Lichida Order Proetida Order Harpetida Order Ptychopariida Order Asaphida Order Odontopleurida Order Nectaspida Trilobite Relatives	o Arthropoda `--o Trilobita |?-Agnostida |?-Eodiscina `--+--o Redlichiida | |--Olenellina | `--Redlichiina |--Corynexochida |--Phacopida |--Lichida |--Odontopleurida `--o Librostoma |--Proetida |--Harpetida |--Ptychopariida `--Asaphida
* Different taxonomies are found, most recently with trilobites contained in Superclass Arachnomorpha in Subphylum Schizoramia.

cephalon (head) that is often perforated by small pores. This often very wide brim is thought to have filtered sediment while feeding. The brim extends backward from the front of the cephalon, and typically has a prominent suture along its anterior boundary. The Harpetida fossils normally show small eye nodules, 12 or more thoracic segments, and small pygidia. They lived from the Upper Cambrian and persisted to the Late Devonian period.

Harpetida became a distinct trilobite order only recently in 2002, after being split from Order Ptychopariida in which they were suborder Harpina. The Harpetids are most often considered to be descended from the Ptychopariids. Moreover, the Harpetida are now often considered to be a member of the Librostoma, a suborder erected by Fortey in 1990 to encompass Ptychopariida, Harpetida, Asaphida, and Proetida based in part on the shared trait of a natant hypostomal attachment (i.e., a hypostome mouthpart not anchored to the anterior doublure).