The octopus belongs to a subclass of cephalopods. They are symmetric, with two eyes and four pairs of arms (the reason they have got the name octopus, which means eight).
Even though the octopus is a cephalopod, it is very different from its relatives such as oysters and snails. It is more closely related to the squid.

The octopus doesn’t have a shell; it has a hard beak, with its mouth at the centre. Since they don’t have a skeleton they can squeeze through narrow places. They inhabit the ocean, favouring coral reefs.

What if you see an octopus underwater?

If you meet an octopus under the water, move away as fast as possible. They might not look dangerous, but there is one kind of octopus, called the blue ringed octopus, which is deadly.

How does an octopus defend itself?

For self defence the octopus can hide, flee fast, expel ink or they can even use color changing camouflage. The octopus can change its colour from red to grey, yellow, dark or greenish. On their back they have a kind of muscular siphon. Water comes in the siphon, and the octopus takes the oxygen from it. This sucking siphon helps it to move fast through the water. The octopus then expels a strong jet of water, which helps it to bounce back. In that way, the octopus can run away from a predator which has come too close.

Octopus walk on their arms?!

The octopus moves by crawling and swimming. When they want to travel slowly, they tend to crawl with some swimming. When they are helped by jet propulsion, they move really fast, but even then they use swimming and walking.
When they crawl, they actually walk on their arms. Usually they use many legs at once, on solid and soft surfaces. Some recent research from 2005 showed that some octopus can walk on two arms.

This way of moving (locomotion) helps the octopus to flee from a potential predator. Moving in this way also helps the octopus to catch its prey. The octopus eats mostly crabs and fish, but when it is hungry it catches everything.
For eating, the octopus uses its strong jaws, which looks like a beak of a parrot. Nevertheless, it can bite strongly and at the same time it can inject its poison. That poisons liquid helps it in disabling its prey.
Its long arms make the octopus look unusual and they are in constant movement. On its arms it has sucking holes, and with these it grabs its prey and squeezes it firmly.