The genera of Cyclopygidae are grouped into the following subfamilies: The extinction ending the Ordovician was one of the most radical for life to have experienced, and the trilobites were heavily affected.

[3] In a few species of the genera Cyclopyge, Microparia, Ellipsotaphrus, Pricyclopyge and in Symphysops the eyes are merged in front of the head creating a visor.

Monocular trilobites are always younger than closely related species with normal paired eyes, and is an example of a trend that occurred several times in parallel.

Only in Pricyclopyge binodosa several stages in this development can be seen as a consecutive series of subspecies collected from successive zones in the late Arenig to the Llanvirn.

Hence, cyclopygids are considered to have been confined to deeper water, swimming at the lower limit of the photic zone (or mesopelagic),[1] but still high above the benthic species they were deposited with.

This is also evidenced by the presumed present of bioluminescent organs on the third thorax segment of Pricyclopyge, which also occur on the functional underside of extant mesopelagic species.

[3] Very large, convex eyes and a narrow zone of thoracic pleurae are typical for all Cyclopygidae, and are indications of a pelagic lifestyle.