Cephalopods: underwater ears

If we still think that the ocean is a world we know, it’s a mistake. Many mysteries are yet to be resolved. For example, Taiwan’s new investigation shows that cephalopods – about 700 species of squid, octopus, cuttlefish and nautiluses – can hear sounds underwater. The octopus can hear sounds between 400 Hz and 1,000 Hz, and the squid can hear a wider range of sounds between 400 Hz and 1,500 Hz. Experiments with blind octopus suggested that these are capable of locating the sounds produced by boats or by tapping on a tank. However, Hong Young Yan, a sensory physiologist of the Taiwan National Academy of Science in Taipei, discovered that octopus and squid could be using another organ called the statocyst – sacs that contain a mineralized mass and sensory hairs – to register sounds. The team of scientists had to overcome many obstacles during their research. For example, the common way of proving that an organism can hear is by measuring how its nervous system responds electrically to sound. But this can require attaching electrodes directly on the exposed nerves, a procedure that could damage the delicate molluscs. The next step, Yan said, would be to investigate what types of sounds cephalopods can hear.