Cyclopygidae  Cyclopygidae is a family of asaphid trilobites from the Ordovician. Cyclopygids had an extratropical distribution, and there is evidence that they lived in darker parts of the water column (around 175m deep). Cyclopygids are characterized by enlarged eyes, with a wide angle of view, both horizontal and vertical, reminiscent of the eyes of dragonflies. These typically touch the glabella directly on the side. Cyclopygids all lack genal spines, but "Symphysops" carries a forward directed frontal spine on the glabella. It is presumed that at least the members of the genus "Pricyclopyge" swam upside down and had bioluminescent organs on the third thorax segment. Cyclopygids had between 7 and 5 thorax segments, a wide and stout axis, and short side lobes (or pleurae). 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. Those with pelagic or deep water benthic life styles (such as species in Olenidae and Agnostida) died out. Also those trilobites having planktonic larvae became extinct, and these include most of the superfamilies in the order Asaphida, save for Trinucleoidea. A reduction in diversity already occurred before this major extinction, but many families persisted into the Hirnantian, and it is possible that they would quickly have been restored to their former diversity. The crisis that started the Silurian must have exceptionally severe, and was associated with low oxygen levels in the oceans after an ice age. Cyclopygids have particularly large eyes with a wide angle view, also vertically, that occupy most of the free cheeks, and the fixed cheeks absent or reduced to a very narrow strip at the sides of the glabella, and a zone between the both eyes. In the earliest cyclopygids ("Prospectatrix") the eyes are less enlarged, but in some later taxa, eyes are so big they have even fused. The most backward lobe of the glabella (the occipital ring) cannot be identified, except in the Ellipsotaphrinae subfamily. Further furrows crossing the glabella may be absent or are reduced to pairs of slight depressions.