Insights into the genetic program of compound-eye formation by an injured phacopine trilobite

There are numerous reports of trilobites that survived macrophagous attacks and whose injuries healed. Significantly, rarely observed, however, are such repaired injuries to the head or especially to the eyes. Here, we report and interpret the healed laceration of a phacopine trilobite eye, revealing details about the genetic program that established the order of lens arrangement in a schizochroal eye. The first and superordinate level is the arrangement of the lenses in vertical and spiral-horizontal rows, which not only seems to be a forced arrangement as a result of eye growth, but which follows a genetically determined program since the order of the lenses is completely restored in one step, even after the visual surface has been destroyed completely. The size of the lenses, and thus their light-gathering capacity, is more flexible and interacts with the context within the pattern of the lenses. The origin of the lesion remains unresolved.