From BBC Earth News : The Cephalopods Can Hear You
"The discovery resolves a century-long debate over whether cephalopods, the group of sea creatures that includes octopus, squid, cuttlefish and nautiluses, can hear sounds underwater.
They discovered that the octopus can hear sounds between 400Hz and 1000Hz. The squid can hear an wider range of sound from 400Hz to 1500Hz, they report in Comparative Biochemistry and Physiology, Part A.
"That indicates that squid have a better hearing capability than the octopus," says Yan. "Interestingly though, both species hear best at a frequency of 600Hz."