Sharks don’t fly. But squid do.
Squid move by pumping water in and out of their bodies. Propulsion comes from using the water itself, sucked into the mantle and squeezed out through a smaller tube called a siphon in a series of strong pulses. By finely manipulating their siphons, squid maintain precise control the water stream: volume, intensity, and direction. All cephalopods carry siphons, even the lumbering octopus, but squid get the most mileage from them.
Water is heavy, so you’d expect slow acceleration from a squid. Not so: powerful rings of muscle surround the mantle, squeezing a huge amount of water through the siphon and creating large accelerations. They’ve also got a secret weapon for emergencies: a lightning-fast escape mechanism. It’s similar to a lobster’s caridoid reflex: a highly specialized nerve structure called a giant axon, a single supersized nerve fiber thicker than a human hair running down the mantle. Its unusual size facilitates the extremely rapid transit of nerve signals to all the muscles of the mantle, so that the maximum amount of water will shoot from the mantle and jet the squid away. The giant axon is a way to translate a simple imperative (“Run!”) into a complex escape response.
The waterborne jet propulsion of squid has been well known for centuries. Since the 1800s, observers have described squid gliding above the water. It was a marine legend, but a recent survey recorded a group of squid off the coast of Brazil doing more than gliding. A fan of 6-inch silver missiles burst from the water and accelerated away, trailing streams of high-pressure water. A second report concerning Japanese squid shows the same capability in ocean-going animals best known as a fishery. The aerodynamic details are not yet completely understood, but jet propulsion allows a flying squid to do something flying fish cannot: accelerate in the air. The Brazilian species Sthenoteuthis pteropus accelerates at more than two g’s. However, fuel runs out quickly—limited by how much the mantle can store—and such brief acceleration can’t get the animals past about 8 miles per hour while airborne. It’s a rare testament to the power and grace of these animals—a phenomenon few people have ever witnessed.
From The Extreme Life of the Sea, Stephen Palumbi and Tony Palumbi, Princeton Press, 2014