Science in Pajamas: Swimming Squid
Squid, which are similar to the octopus, have eight arms and two tentacles. The arms, called cephalopod limbs, resemble those on an octopus with suckers along their length. The two extra tentacles have suckers only their ends, and are meant to capture food such as fish and crabs.
Its powerful muscles contract to force out jets of water that propel it in the opposite direction that they’re facing - so it swims backward in a zigzag formation. As a strategy to avoid predators, it can shoot out an inky fluid made from melanin particles called sepia that creates a dark cloud, allowing it to create a diversion and flee to safety.
See the quick movements of a squid for yourself with a homemade creation!
What you'll need:
squirt cap (the type that comes on sports drinks works well)
Fill the bathtub with water. Then, fill the balloon with water, and while you keep the neck pinched closed, have a friend stretch the lip up over a closed squirt cap. Hold your balloon “squid” underwater one end of the tub or sink, open the cap nozzle, and let go. Water will shoot out of the bottle and propel the balloon in the opposite direction - mimicking a real squid!
If you're interested in the detailed physics behind this movement, here's a great resource.
Resources and References:
Littlefield, Cindy A. Awesome Ocean Science: Investigating the Secrets of the Underwater World. Williamson Books, 2006.
Zych, Ariel. “Jet Propulsion Locomotion of Squid and Octopus.” Science Friday, www.sciencefriday.com/educational-resources/jet-setting-cephalopods/.
Watson, Stephanie. “How Squid Work.” HowStuffWorks, HowStuffWorks, 1 June 2007, animals.howstuffworks.com/marine-life/squid2.htm.