You would think that
squids would be happy just to be odd-looking,
funny-eyed,
ink-squirting, many-armed, tenacious predators and superb
camouflage artists. It would be reasonable to assume that being able to
regenerate their arms and tentacles, complete with hooks and powerful suckers, would be enough for them. You might suppose that they would be satisfied with their fearsome reputations and the numerous legends told about
them. But no, in their never-ending quest to become the most bizarre creatures on the planet, they had to go one better: they had to invent
jet propulsion. The little showoffs.
How It Works: All cephalopods use jet propulsion, but squids are undoubtedly the best at it and are built almost like fighter planes to make propulsion more efficient. Water is drawn in from the free edge of the mantle and expelled through a siphon, or funnel, on the squid's underside. First, the mantle walls expand to draw the water into the mantle cavity through the collar of the mantle, while the siphon is closed. The head is then pulled towards the body, sealing the intake with a set of matching ridges and depressions, and valves extending from the sides of the siphon. The mantle cavity's strongly muscled walls then contract sharply, driving water at high speeds out the siphon. The flow of water can be controlled through a muscle valve just inside the siphon's opening, and the siphon can also be aimed forward or backward by the squid.
These jets are extremely powerful, and using them, squids are capable of swimming at amazing speeds. Common Pacific squids can travel at 5 to 8 MPH. Larger species have been seen moving at around 20 miles per hour, occasionally overtaking ships. When moving at these speeds, the arms are held tightly together, turning the squid into a highly streamlined cigar shape, and the fins are held close to the body. Note that when jetting, most cephalopods tend to swim backwards - body forward, tentacles at the rear - although they can move in either direction by turning the siphon.
Strandings: This habit of swimming backwards at high speed is not always a healthy one. While squids have an extremely wide angle of vision, they cannot see directly to the rear, and squids quite often strand themselves in shallow water. To make matters worse, when they do strand themselves they tend to react by working their jet at the highest pressure, with the siphon pointed seaward, driving themselves firmly into the sand. Even when they are picked up by humans and flung back into the sea, they immediately jet themselves back toward the beach and wedge themselves into the sand again. It seems that squids, while more impressively designed than octopuses, are hardly the brightest of the cephalopods.