- Ptychopariida
Taxobox
name = Ptychopariida
image_width = 230px
image_caption = "Elrathia kingi"
regnum =Animal ia
phylum =Arthropod a
classis =Trilobita
subclassis =Librostoma
ordo = Ptychopariida
ordo_authority = Swinnerton, 1915
subdivision_ranks =Suborder s
subdivision =
*Suborder Ptychopariina
**Superfamily Ellipsocephaloidea
**Superfamily Ptychoparioidea
*Suborder OleninaPtychopariida is a large, heterogeneous order of
trilobite containing some of the most primitive species known. Many date to the LowerCambrian period, but the order was extant through the UpperOrdovician period. Many of the offshoot species are difficult to classify in this single order.These trilobites have facial sutures that run along the margin of the glabella (central portion of the head) to the shoulder point where the
cephalon meets thethorax . These sutures outline the glabella, or the main, central part of the head that doesn't include the free cheeks. The eyes are medial along the glabella on the suture line (however, some species have no eyes). Genial spines stretching back from either side of the cephalon are often present. Thefossil s of the moults of these trilobites can often be told from the fossils of the actual animals by whether or not the free cheeks are present, as in the moults, the free cheeks are no longer attached. Bladelike genial spines are often present.The thorax is large, and is typically made up of eight or more segments. The thorax is usually much longer than the tail section (
pygidium ), which is usually small. In some species, the pygidia are outlined with a flat border.The subclass Librostoma was recently created to encompass several highly related orders (Ptychopariida,
Asaphida ,Proetida ,Harpetida , and possibly thePhacopida ). They are now known as the "Librostome Orders". The Proetida and Harpetida were originally included in order Ptychopariida.References
* [http://www.es.mq.edu.au/mucep/trilobites/ptychopa.htm Order Ptychopariida]
* [http://www.trilobites.info/index.html A Guide to the Orders of Trilobites] By Sam Gon III
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