The giant squid's eye is as big as a basketball, the largest in the animal kingdom

A giant squid's eye can reach roughly 27 centimetres (nearly 11 inches) across, far larger than any other living creature's. Researcher Dan-Eric Nilsson and colleagues argued in 2012 that the huge eye evolved to spot one specific thing in the pitch-black deep ocean: the faint bioluminescent glow stirred up by an approaching sperm whale, giving the squid precious extra seconds to flee.

— Dan-Eric Nilsson et al., A Unique Advantage for Giant Eyes in Giant Squid — Current Biology, 2012