- Suborder Ptychopariina
- Superfamily Ellipsocephaloidea
- Superfamily Ptychoparioidea
- Suborder Olenina
Ptychopariida is a large, heterogenous order of Trilobites containing some of the most primative species known. Many date to the Lower Cambrian period, but the order was extant through the Upper Ordovician period. Many of the offshoot species are difficult to classify in this single order.
These trilobites have facial sutures that end along the rear margin of the cephalon (head + free cheeks) along the line where the cephalon meets the thorax. These sutures outline the glabella, or main part of the head (not including free cheeks). The eyes are medial along the glabella on the suture line (however, some species have no eyes). The moults of these trilobites can often be told from the actual fossils by whether or not the free cheeks are present, as they are not attached to the moults. 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. The pygidia are often outlined with a flat border.
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