Morphology of Lower Cambrian Lobopodian Eyes and Their Evolutionary Significance  

Evidence of fossil visual systems is crucial for understanding the origin and evolution of eyes.  This study investigated the rare visual organs of Cambrian lobopodians from the Chengjiang lagerstätte, Kunming, China, using a new technique, Infinite Focus Microscopy, which can reproduce 3D topographic information.  The eyes of Hallucigenia fortis and Cardiodictyon catenulum are reported for the first time, and the morphological details of the eye of Luolishania longicruris are revised.  The eyes of H. fortis and L. longicruris are composed of three visual units, each of which has a pigment cup and a ‘lens’. The eye of C. catenulum only has a single visual unit with a deeply sunken ‘lens’. Cladistic analysis among Cambrian lobopodians suggests that their visual systems may have evolved from an eyeless condition to a single-unit eye and then to a tri-unit eye.  The eyes of H. fortis and L. longicruris are not similar to the simple eyes (ocelli) of tardigrades and onychophorans, but resemble arthropod lateral visual organs, especially the stemmata of myriapods.  They appear to represent the ancestral visual systems of arthropods and perhaps gave rise to the two major types of arthropod lateral eyes (lateral compound eyes and lateral simple eyes). Calculation of their focal distance suggests that the eyes of L. longicruris and H. fortis were capable of forming an image.