The first eyes probably appeared long before the Cambrian explosion that occurred from 541 million to 530 million years ago. Some of the earliest renditions might have been a simple pit eye, a kind of pit of tissue lined with light receptors, or what scientists call an eyespot, a simple region that detects light. Mossy New Caledonian gecko is the largest gecko species ever recorded—individuals grow up to 14 inches long. Wood louse spider: This species belongs to a relatively small number of spiders that have six eyes instead of eight. They lack the “principal eyes,” which convey color vision and higher spatial acuity in most species.