字幕表 動画を再生する 英語字幕をプリント Today Jonathan investigates the amazing world of suckers! Cephalopods! Welcome to Jonathan Bird's Blue World! An octopus is on the prowl, looking for an unsuspecting fish to pounce upon. A cuttlefish is hunting with mesmerizing colors to distract its prey. A school of reef squid hover in the water column. What do these magnificent animals have in common? They are all cephalopods. Cephalopod means “head-foot” because this animal's head (the part with the eyes) is connected to its feet. The part out in front that looks like a head is actually the body. And in fact biologists don't call those things feet, they are called arms. So cephalopod is actually a terrible name, but it's what we have got. Squid, octopods, cuttlefish and nautiluses are all members of the class cephalopoda, but the really weird thing is that cephalopods are mollusks. So they are related to animals like snails and clams, which seems a little crazy. This is based mostly on their internal construction, not their outward appearance. Perhaps the most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. The octopuses do not have shells at all. The squid have a small internal shell. Nautiluses are the only cephalopods with an external shell. Nautiluses are found in the South Pacific and Indian oceans, typically in deep water. Cephalopods have well-developed nervous systems, much more sophisticated than other mollusks. And they can be quite inquisitive. The cephalopod eye is one of the most notable examples of convergent evolution in all of the animal world, because this eye evolved from completely different ancestors than the eyes of mammals, yet it turned out to function in almost the exact same way. Cephalopods, therefore, have extremely good eyesight. Of course the most well-known of the cephalopods are the octopuses, named for their eight arms. They are masters of disguise, able to change colors and skin patterns instantly. With no shell, or bones the octopus can fit through tiny holes. They make terrible pets because they can escape from virtually any aquarium! The octopus has a mouth with a beak used to bite prey. A hunting octopus often balloons over a rock to trap a fish. Then it will use venomous saliva to kill the prey when it bites. But the Blue-Ringed octopus of the South Pacific has venom so powerful that the bite of this octopus is lethal to a human. The mimic octopus is said to mimic other animals in order to hunt or evade predators. This one has a convincing flounder imitation going on, but it's unclear how looking like a flounder is advantageous. It might just be the most efficient way to swim and stay camouflaged—convergent camouflage if you will. A coconut octopus in Indonesia carries a shell so that when the need arises, she can hop inside and hide. This clever behavior makes the octopus a tool user, putting her in a category of animals considered more sophisticated and intelligent, like monkeys and dolphins. In the cold water of Puget Sound, a Red Octopus is carrying a crab home for dinner, walking on the tips of its arms. That takes coordination! Nearby, a Giant Pacific Octopus breathes by drawing water into its mantle, a cavity in its body and squirting it back out through a siphon. Not only does this move water over the gills, but it gives the octopus the ability to squirt water. The siphon can be used for jet propulsion, squirting an octopus away at high speed. A reef octopus in the Caribbean not only squirts away from me, but leaves a smoke screen behind in the form of an ink cloud. Squid and cuttlefish are similar to octopuses, but their small internal shell makes them rigid and torpedo-like. So, while the octopus often crawls along the bottom, the squid and cuttlefish like to jet. In the North Atlantic Ocean, Longfin Squid cruise through the New England shallows. But when they get annoyed by my camera…they can produce ink too. More than 8 thousand miles away from New England, the waters of the Philippines are warm and clear. After the sun goes down, a Flamboyant cuttlefish comes out to hunt. While the octopus has eight arms, the cuttlefish and squid actually have ten. Eight of them are of the same length, while the other two are extra long, and used to grab prey. These two additional arms are called the tentacles. Cuttlefish are often quite curious, and sometimes come right up to my camera for a look. Their skin patterns change rapidly thanks to skin cells called chromatophores. At the New England Aquarium in Boston, there's an exhibit where you can watch cuttlefish up close. And when you look carefully, you can see the chromatophores working. At feeding time, the cuttlefish pay close attention, and they turn on the camouflage. Then the cuttlefish strikes. Even slowed down to one quarter speed, it's lighting fast. With a high speed camera, a flamboyant cuttlefish blah blah In another tank, a Giant Pacific Octopus guards it eggs. All cephalopods lay eggs to reproduce. Octopuses tend to guard their eggs. Back in Indonesia, the Coconut octopus is releasing thousands of baby octopus hatchlings from her clutch of eggs. She carried them around for months while they incubated. Squid and cuttlefish do no such thing. The Atlantic Longfin squid lays its eggs like most squid…cigar shaped bundles of eggs attached to the rocks or kelp and left to fend for themselves! The Flamboyant Cuttlefish eggs are about the size of a pea--laid on a rock. Soon a baby cuttlefish is born. The cephalopods are an amazing group of animals. It's hard to imagine such advanced animals being closely related to such primitive mollusks as the conch. Cephalopods can change color and texture with chromatophores, they have extremely sharp eyesight, multiple arms that are capable of complex tasks, and they are clever enough to use tools! They are definitely one of my favorite inhabitants of the Blue World.