Which ocean animal has the largest eyes of any known animal?

The colossal squid has the largest eyes of any known animal.

Its eyes can be estimated at roughly 27 centimetres across, although exact measurements are difficult because intact giant specimens are rarely recovered. Large eyes are useful in the dark deep ocean, where they can detect faint light and help the squid notice approaching predators or prey.

The colossal squid lives in the Southern Ocean and is known mainly from damaged specimens, stomach contents, and a small number of captured animals. It has a compact, heavy body and swivelling hooks on its arms and tentacles, unlike the toothed suckers of many other squids.

The giant squid can also have enormous eyes and was long associated with the record, but current anatomical comparisons place the colossal squid first. Size estimates for both species are complicated by flexible bodies and the effects of pressure changes after capture.