(the plural of ocellus) are a type of simple eye, or eyespot. They are photoreceptive, but very simple; differing from complex eyes with compound lenses, ocelli cannot morph the sensation of light into a complete image, and are utilized to sense movement and the absence and presence of light. Cnidarians are the most primitive extant animals that possess these simple eyespots; however, they exhibit an extremely wide range of phototactic behavior that ranges in complexity alongside the variation in ocelli. Cubozoa rhoplaial structures and their various types of ocelli are the most complex within the Cnidarian phyla, and resemble the advanced image-forming eyes of squids, octopuses and vertebrates. It has been observed that the removal of some of the rhopalia in the species Aurelia results in a period of two weeks to complete regrowth, with only subtle loss of size and pigmentation but virtually identical function. Even the organ's ocelli, of both types, are capable of being fully regenerated as long as at least two rhopalia are left intact prior to amputation of the others. This exhibits that parts of the nervous system that would be considered precious and vital by most other living things can be regenerated in scyphozoan medusae . However, this has not been tested in cubozoans, which have the most elaborate nervous systems within Cnidaria, specifically concerning their visual capacities. See also Nerve net References External links Cnidarian anatomy Articles containing video clips