Identity

Where to find them?

You can find octopuses in every ocean of the world. Depending on the specie, you will find them in coastal marine waters or in deep water. 

They live most of the time hidden in small holes and cracks, and all species are living exclusively in salt water.

How long do they live?

Some species have very short life (with life expectancy about 6 months), but other species may live up to 5 years.

What size are they?

The giant specie (Giant Pacific Octopus) is the largest one and can reach up to 9 meters with an arm span. The smallest specie is around 2,5 cm (Octopus wolfi).

How many species?

There are about 300 different species of octopuses.

How do they reproduce?

They practice exertnal fertilization. When they reproduce, the male uses a specialised arm called "hectocotylus" to introduce spermatophores into the female's cavity. The cavity where the sperma goes is the funnel that the female uses to breathe. Sometimes, the male can also hand the sperm to the female, which she always accepts with one of her right arm (researchers still ignore why). 
Except only one specie (larger Pacific striped Octopus) who can reproduce more than one time, after mating all the males go away to die. Regarding the females, they lay from 300,000 up to 400,000 eggs, and they will devote all the rest of their own life to tend and protect them, they even will stop eating at this point. From the moment the female octopus lays eggs a biological mutation starts and her body slowly destructs itself until they die. 

How & what do they eat?

Octopuses eat mainly crustaceans, worms, crabs, spider crabs, other molluscs and sea snails. (It rejects the shells.)
Depending the specie they hunt they will adapt hunting technic to them. 

Most of the time, octopuses hunt by moving on the bottom and sometimes they search inside the crevices. They also can use propulsion to their prey, using their arms to pull it and their tentacles to restrain it. They can use others technics like: spreading a paralysing saliva, or using their suckers on shells to forcibly open them, or even making a hole to the shell so they can inject a nerve toxin. Finally, some octopuses are even able to swallow their whole prey.
One specie can even lure their prey with photophores and make them come to their mouth.
Regarding its growing, octopus will have a proportional appetite. 

How do they move?

When they are not in a hurry, octopuses crawl relatively slowly. Otherwise they can use jet propulsion or backward swimming to move faster. They are also able to use their tentacles and their arms to pull or push them and move. It's interesting to know that when they move like that their heartbeats are accelerating and they will need 10-15 min after to recover from it. 
One more time, regarding the specie they belong to, octopuses have different technics and abilities to move in the sea. 

Who are their predators?

As many other fishes, one of the big predator of octopuses is unfortunately human. 
Apart from that, octopuses are eaten by fishes, seabirds, sea otters, pinnipeds, cetaceans, and other cephalopods. To escape, they hide or disguise themselves by camouflage and mimicry. They also use ink clouds to protect themselves.
If needed under attack, they can detach one of their arm and move away. Later, octopus will be able to replace the lost limb.

What people usually ignore?

The reproduction of octopuses has been studied in only a few species.
We also still ignore why during mating the female always take the sperm with one of her right arm?
We ignore many things about their intelligence, capacities and abilities (for example regarding their change of colors).
We don't know up to which depth they can go?