Sunday, 1 May 2011

Report Text_Octopus

Octopus

Armed and Extremely Brainy

Octopuses live in oceans and seas around the world. They have eight arms, no backbone, three hearts, and a jumbo-sized brain. They can do some amazing things. They can squeeze their bendy bodies into narrow cracks, change color in a matter of seconds, and outwitpredators with a clever disappearing act. They’re smart, too. They can learn new tasks and later remember what they learned. That’s something that even we humans sometimes find challenging!

Octopuses and Their Spineless Cousins

Octopuses are invertebrate animals known as mollusks. Their closest relatives are squid, cuttlefish, and chambered nautiluses, all of which belong to the mollusk group called cephalopods. The wordcephalopod means “head-foot” and describes an octopus’s body quite well. The octopus’s flexible, boneless body is basically just a head with feet (arms) jutting out of it.

Octopuses Past and Present

Scientists believe that octopuses began to evolve more than 400 million years ago. Their ancestor had a shell and looked something like a snail. Today, there are 289 species of octopus. None of them has a shell. The largest variety of octopus species are found in waters near Australia.

Small, Medium, and Large

Some species of octopus live in shallow water while others live in the deepest parts of the ocean at depths up to 5,000 m. Most species stay close to the seafloor. One of the smallest species is the California Lilliput octopus, which measures about 2 cm across, or about the width of a bottle cap. The common octopus is a medium-sized octopus. A typical size is about 50 cm, or roughly the size of a large pizza. One of the largest, the giant Pacific octopus, can grow to a whopping 9 m. It’s so big that with its arms stretched wide it would barely fit into a two-car garage.

Making More Octopuses

When octopuses mate, the male octopus uses a special arm called the hectocotylus to place little packages of sperm inside the female’s body. The sperm fertilizes the female’s eggs. The female may lay up to 100,000 eggs. She drapes clusters of eggs from the ceiling of herden. She squirts water from her siphon on the eggs to give themoxygen. She also cleans away algae or dirt clinging to the eggs. The eggs hatch in four to eight weeks, depending on the species. The newly hatched babies look like tiny versions of their parents.

Going It Alone

Female octopuses usually die soon after their eggs hatch. Each baby octopus is on its own. It floats near the surfaceand eats anything it can fit into its mouth. Many young octopuses are eaten by fish and other animals, but those that survive grow larger.
After several weeks or months, the young octopuses settle on the ocean floor. They begin stalking small crabs and other prey. It takes several weeks to a year for an octopus to reach adulthood, depending on its species. As adults, octopuses remain solitary. The only time they get together with other octopuses is when they mate. Sometimes they meet for meals, but it’s not a friendly get-together—one of them ends up getting eaten!

No Teeth, No Claws, No Problem!

Octopuses don’t have claws or teeth that they can use as weapons. They have other adaptations and behaviors that protect them from predators. Fish, sharks, and birds who hope to make a meal out of an octopus have their work cut out for them.

Outta Sight!

Finding an octopus is a predator’s first problem. Octopuses like to stay hidden. Some bury themselves in the sandy sea bottom. Then, to make themselves even harder to see, they change the color of their skin so that it matches the seafloor! It takes less than a minute for an octopus to change its color and camouflage itself.

In a Tight Spot

Octopuses can also squeeze themselves into dark, narrow spaces between rocks and coral. Small octopuses even slip into seashells. These shelters, or dens, keep octopuses beyond the reach of most predators.

Scare Tactics

Octopuses use scare tactics when they come across a predator. The mimic octopus, for example, does a great imitation of a venomous sea snake. To do this, the mimic octopus buries six of its arms in the sand. It changes the coloring of the two arms that stay visible to a yellow-and-black pattern. This makes it appear to be the same shape and color as a sea snake. Octopuses that live near the shore sometimes scare away hungry birds by using their siphons as squirt guns.

Inked Out

Octopuses have even more ways of freaking out predators. When face to face with a predator, an octopus can use its siphon to shoot out a dark substance called ink. The inky cloud hides the fact that the octopus is swimming away or burying itself in the sand. By the time the ink clears, the octopus has vanished.

Unarmed but Unharmed

If a predator catches an octopus, the octopus takes drastic action. It lets one of its arms break off! The detached arm dances around and changes color to get the predator’s attention. The predator usually starts eating the arm. This allows the octopus to swim away unnoticed. In time, a new arm grows in to replace the lost arm.

Beware of the Blue-Ringed Octopus

The blue-ringed octopus, which lives near Australia and Japan, is the only octopus that uses venom for defense. A blue-ringed octopus is smaller than the palm of your hand. To many predators, it looks about the right size for a snack, but most predators keep away. The blue-ringed octopus’s markings are a warning that it is poisonous. The venom in its saliva is so powerful that this octopus can kill predators much larger than itself. The venom has killed humans who have handled a blue-ringed octopus or accidentally stepped on one.

Grabbing a Bite to Eat

Octopuses are carnivores that eat small fish, shrimp, crab, lobsters, scallops, mussels, and clams. Octopuses use their long, sucker-covered arms to reach into nooks and crannies and grab prey. The suckers latch on to prey and make escape almost impossible.
The octopus bites into soft-bodied prey with its beak. If the prey has a shell, the octopus uses its tongue-like radula to drill through the shell. It then injects the prey with saliva that paralyzes the prey. The octopus usually carries the prey back to its den so it can eat safely hidden from predators.

Getting a Move On

Octopuses use their powerful arms to creep along the ocean floor as they stalk their next meal. When they need to make a quick getaway, however, they take in a big gulp of water through openings between the mantle and head. Then they force the water out through their siphon. This form of movement is known as jet propulsion.

Octopuses and People

Drawings of octopuses on pottery thousands of years old suggest that humans have been intrigued by octopuses for a long time. Their unusual appearance has inspired myths. One of these myths is a creation myth from Kiribati, an island nation in the Pacific Ocean located northeast of Australia. This myth tells of an octopus god named Na Kika. Na Kika used its many arms to push land from under the sea upward to form the islands of Kirbati.

Pet Octopuses: Only for Experts

Some people keep octopuses as pets. Pet octopuses need special care. They must have a large tank, and water conditions must be carefully controlled. Most people do not have the equipment or knowledge to give an octopus the care it needs. If you want to get a close-up look at an octopus, find out if there is a public aquariumnear you that has octopuses.

Octopus on the Menu

People have probably been eating octopuses as long as they have been eating fish. Octopus is still an important food for many. People all over the world eat octopus, but it is especially popular in Japan and in European countries such as Greece, Portugal, and Spain. People often cook octopus by grilling it, but it is also used in sushi, salads, stews, and rice dishes.

How Smart Are Octopuses?

Scientists who study octopuses have done experiments with captive octopuses to test their intelligence. In one study scientists placed a crab in a clear jar. The octopus could see the food, but couldn’t get at it. After several tries, the octopus figured out how to use its suckers to unscrew the jar lid and get the food!
The next time the octopus was given a jar with food in it, it remembered how to open the lid. Scientists have also discovered that octopuses can learn to find their way through mazes and to recognize the shapes of different objects. Studies like these have led scientists to conclude that probably no other invertebrate is as intelligent as the octopus.


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