Spiders might seem like good contenders for the title of ‘most eyes in the animal kingdom’ but even with an impressive eight, they don’t come close to the record holders. If you’re looking for animals with lots of eyes, the best place to search is under the sea.
Nautiliuses and giant clams (Tridacna gigas) have eyes like pin hole cameras: rather than having a lens, they simply have a hole. This hole functions a little like a pupil, allowing the animals to vary how much light enters the eye. These primitive eyes are not great for building up detailed pictures of the environment, but they can rapidly detect changes in light and shadow. Perfect for detecting movement nearby. Giant clams need this ability because they have colonies of photosynthesising algae living in their bodies. The clams open up to expose these algae to the light, allowing it to grow, but if something dangerous swims overhead they need to snap shut for protection. To do this, they have not one or two but thousands of tiny eyes lining each side of their mantle. However some have argued the eyes are not ‘true eyes’ as they only allow light to pass. In essence, they are photoreceptors.
Scallops on the other hand have a similar physiology, with eyes lining the mantle. With each scallop possessing hundreds of eyes, these eyes also have a lens and a retina, attached with an optic nerve. In addition to this, a reflective layer called a tapetum bounces light onto the retina, enhancing the scallop’s vision. This is essential in the low-light conditions of the deep ocean and a feature also seen in nocturnal animals such as cats and raccoons. Although the scallop’s sight is somewhat more sophisticated than the giant clam’s vision – they still can only really detect changes in light and motion.
Check out this amazing video below of a scallop in action. The blue dots lining the edge are the creature’s eyes!