Chone ecaudata, a sabellid fanworm, has a cluster of two to four ocelli embedded within each side of the brain and a pair of pygidial ocelli on the tail. Both types of ocelli have rhabdomeric (microvillar) photoreceptors. Each cerebral ocellus consists of two cells: sensory and supportive. The latter forms a pigmented cup that encloses the array of microvilli of the former. Each pygidial ocellus consists of a simple plaque of columnar, epidermal cells of three types: photoreceptoral, pigmented, and secretory. A pygidial photoreceptoral cell bears many microvilli, situated below the cuticle in a depression at the distal end of the cell, and two cilia, usually, which project vertically among the microvilli and then bend to lie beneath the cuticle. The cerebral ocelli are more complex and probably more light sensitive than the simpler, more primitive pygidial ocelli. Cerebral and integumentary ocelli are compared in polychaetes and representatives of other phyla, and their evolution is discussed.