Which animal has the largest eyes of any living creature?

The giant squid, with eyes up to about 27 centimetres across - roughly the size of a dinner plate, and several times larger than any other animal's, including whales far bigger than the squid.

That is disproportionate enough to need an explanation, and the best one is sperm whales. Modelling by researchers in 2012 found that enormous eyes offer no advantage for spotting ordinary prey, but they do help with one specific task: detecting the faint glow of plankton disturbed by something very large approaching through dark water, at ranges of over a hundred metres. The eye is not for hunting. It is a predator alarm, and the predator is the only animal that routinely eats giant squid.

The species was photographed alive for the first time only in 2004 and filmed in its own habitat in 2012. Almost everything known about it before that came from carcasses washed ashore and from beaks found in the stomachs of sperm whales, which is a slightly grim way to inventory an animal.