It is known now, through the work of Mooney and others, that the squid hearing system has some similarities and some differences compared to human hearing. Squid have a pair of organs called statocysts, balance mechanisms at the base of the brain that contain a tiny grain of calcium, which maintains its position as the animal maneuvers in the water. These serve a function similar to human ear canals.
Each statocyst is a hollow, fluid-filled sac lined with hair cells, like human cochlea. On the outside of the sac, the hair cells are connected to nerves, which lead to the brain. "It's kind of like an inside-out tennis ball," Mooney said, "hairy on the inside, smooth on the outside."
The calcium grain, called a statolith, enables the squid to sense its position in the water, based on which hair cells it's in contact with at a given moment. Normally it rests near the front of the sac, touching some of the hair cells.
When a squid moves quicklyas it does when it flees an approaching predatorthe heavy calcium stone lags behind slightly before catching up to the hair cells. "Kind of like your stomach on a roller coaster," Mooney said. "The hair cells are very sensitive and can detect the calcium statolith lagging behind, then catching up."
Structurally, the statocyst "is analogous to our auditory system," said Mooney, who began his hearing research while working on his Ph.D. at the University of Hawaii. The statocyst, he thinks, "is on its way to becoming an ear" like the more familiar ears of vertebrates.
But to what extent does it function as an ear? "One of the obvious questions is, 'Can this acceleration-sensing 'ear' to also detect sounds?' Then, if they can hear sounds 'Do squid hear their predators coming?' " Mooney asked.
|Contact: Media Relations|
Woods Hole Oceanographic Institution