"Most polychaetes have some type of photoreceptor or eyes. Eyes are generally located on the . The complexity of eyes varies from simple pigment cups or , to well developed camera-type eyes, to compound eyes analogous to those found in arthropods (Eakin and Hermans 1988). Ocelli occur in a wide range of polychaete taxa. They can be as simple as two cells—a sensory cell and a pigmented support cell ... Other forms of ocelli are more complex but still may be composed of only a few dozen cells. They probably perceive information about light direction and intensity. In certain Phyllodocica, particularly the swimming predatory Alciopini, the eyes are probably capable of forming an image. The eyes of Alciopini can be up to a millimetre across and so large that they protrude laterally from the head and press into the brain. They consist of a primary retina containing thousand of cells, a secondary retina overlain by a lens and other accessory structures (Hermans and Eakin 1974). Compound eye, which evolved independently of those of arthropods, are found on the radiolar crown of some ..."