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 outwit predators 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 word cephalopod 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 her den.
She squirts water from her siphon on
the eggs to give them oxygen.
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 aquarium near
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.