Like other cephalopods, Octopus have four pairs of arms and two eyes and are bilaterally
symmetric. They have a hard beak that has a mouth at its centre. They do not have a
skeleton and this allows them to squeeze into very small and tight locations.
They are found in many diverse oceans such coral reefs,pelagic waters and around the
ocean floor.
Octopus defend themselves from predators in a number of ways this includes the expulsion
of ink, using camouflage, deimatic displays, moving quickly through water and hiding.
They can move by crawling or swimming. When they swim they trail their eight arms behind them
as they do so.
They are venomous organisms but only one type of octopus is really deadly to humans, that
is the blue-ringed octopus.
There are around 300 species of octopus and they do not have a long life expectancy and
live for as little as six months.However, larger species can live for up to five years
in specific circumstances.
The reason for such a short life span is that they die in the reproduction process. Males
can only live for a few months after mating and females will die shortly after their eggs
hatch. Whilst taking care of the un-hatched eggs, they do not eat and eventually die of
starvation.
Octopuses have three hearts, two of which pump blood around their gills whilst the third
heart is a systemic heart which pumps blood around the body. Their blood contains a copper-rich
protein that enables the blood to transport oxygen.
When Octopus eject ink, they give out a thick, black ink in a large cloud that helps them
to escape. The colouring agent that they have is melanin which is the same chemical that
humans have for their hair and skin colour.
Their camouflage is helped by certain specific skin cells that change the colour, opacity
and reflectivity of the epidermis. They can also use their colour changing ability to
communicate of warn other octopus. Other species such as the mimic octopus, can also mimic
more dangerous sea snakes, eels and lion-fish as another defence mechanism of theirs.
They reproduce by using a specialized arm to transfer packets of sperm from the terminal
organ of the reproductive tract into the female's mantle cavity. In some species, the female
octopus can keep the sperm alive inside her for weeks until her eggs are mature. After
they have been fertilized, the female lays up to 200,000 eggs.
Species of Octopus that live on the ocean floor mainly feed on crabs, worms, and other
molluscs such as whelks and clams. Those species that swim the open-ocean eat mainly prawns,
fish and other cephalopods.
Octopus kill their prey by using a paralysing saliva before dismembering it into small pieces
with their beaks. They feed on shelled molluscs either by using force, or by drilling a hole
in the shell, injecting a secretion into the hole, and extracting the soft body of the
mollusc. Large octopuses have also been known to catch and kill some species of shark.
The largest species of octopus is the giant Pacific octopus, which weighs in at around
15 kg, with an arm span of up to 4.3 m. The largest specimen of the Giant Pacific Octopus
weighed in at 71 kg.