Shy Shadows: Octopus and Squid
1 As I watch, a shadow glides toward the ocean floor where it disappears into rocks which are pockmarked with holes and craters. I have had a close encounter with the world’s first carnivorous predator. No, it is not the shark. My encounter has been with an octopus.
2 Biologists have identified a class of the Phylum mollusca (mollusks) as the first active, carnivorous predatory animals. The class is named cephalopoda (Latin and Greek for"head-foots"). The class cephalopoda is limited to marine animals and has six hundred living species including those of the octopus and the squid.
3 Luckily for me, the appetites of the two largest mollusks do not usually make them look at humans as dinner. These two prefer to dine on fish and crabs, being in the first active, or hunting, family of animals. The predatory animals, the squid and the octopus, display inimitable behaviors and body systems.
4 Both of these marine animals are shy and choose to stalk their prey quietly. When threatened, the octopus has been observed actually growing pale in color. This behavior provides an illusion of greater size and is a defensive action for the octopus. The octopus can also change colors to blend into its surroundings. A different defensive behavior or strategy that the octopus and the squid share with cephalopods is the ability to squirt a cloudy fluid which cuts down on the ability of possible attackers to see them.
5 These strategies, as well as the tendency of the octopus to hide in enclosed spaces (rocks, sunken ships, or reefs), are necessary for survival. Cephalopods may have either an external shell, an internal shell, or as in the case of the octopus—no protective shell at all. So the brain, the stomach, the arms, and all the other soft tissues are exposed and vulnerable to injury. The squid has an internal shell which gives it the distinctive streamline shape. The unprotected octopus has a rounded almost undefined shape, undefined, that is except for the body feature that people think of when they think of an octopus or squid: the arms or tentacles.
6 The arms are the most recognizable features of the octopus and the squid. The octopus gets its name partly from its number of arms: octo is the Latin word for "eight." Both the octopus and squid use their arms for capturing and eating food. They bring the food to their beaklike jaws to cut it into smaller pieces. The octopus also uses its arms to move along the ocean floor as well as using a flow of water through its body to propel it along. It can take water into its body and then squirt the water out, propelling itself at a rapid pace. The squid differs only in that it does not use its arms to move. Instead, the squid stays suspended between the ocean floor and surface and moves only by water propulsion. In fact, since the squid has no other means of movement, its body shape and muscles have become well suited to the water-propulsion method, making it one of the fastest invertebrate (animal with no backbone) marine animals.
7 The squid is also one of the largest marine animals. Or rather, the Architeuthis, the giant squid, is the largest invertebrate. There are theories that the old stories of sea monsters were spun by sailors who had seen giant squid. These squid can grow up to seventy feet, and they have the largest eyes of any animal on earth. Oddly enough, no one has ever seen a living giant squid in its natural environment. Either it hides well, or the stories of sea monsters have a hold on even the most adventurous sea explorers. There are scientists now conducting new research off the coasts of New Zealand and Australia, trying to learn more about this intelligent behemoth of the deep.
8 Keeping an eye out for the marine creatures that do not turn down humans for lunch, I slowly head toward the rocks where the shadow has hidden. My time is running short, along with the air in my oxygen tanks. I must go back to my own world, away from the hushed, dim world of the cephalopods. Before I go, I catch a last glimpse of the creature, turned a reddish color to match the rocks behind it. The fragile octopus has every reason to be shy. It has no shell to retreat into. . .