The arms of the octopus can "taste" as well as touch. Studies have recently found that the suckers have cells that can detect chemicals. So when the octopus explores dark crevices with its arms, places that it cannot possibly see into, it can tell by both touch and taste if what it encounters is dangerous, potential prey, or neither.

The blue-ringed octopus (Hapalochlaena lunata) is just 10cm long. It is a very pretty animal and swims in an elegant manner among the coral reefs in the Pacific and Indian oceans. However it has a venomous bite potent enough to kill an adult human in just 15 minutes.

The smallest octopus found so far is Octopus wolfi, whose common name is the Star-sucker octopus. It has a mantle length of just 2.5cm, and with its arms extended can just about reach 5.0cm.

The giant Pacific octopus, Enteroctopus dofleini, also known as the North Pacific giant octopus, can be 5m long and weigh up to 50kg. It is found on the coastal shelves of the western U. S. and Canada. It is a bottom dweller found at all depths down as far as 1500m or more. It eats molluscs, crustaceans, fish, and has even been reported to catch and eat sea birds. It is popular in aquaria, and is caught for seafood, and as bait. The female lays her thousands of eggs in a sealed up burrow or crevice and looks after them washing them with a stream of water and grooming them to keep them free of parasites. The eggs can take eight months to hatch depending on the water temperature, and during all this time she does not feed. Soon after the eggs have hatched she dies. Although her size is large her life span is usually less than four years.

Eledone sp. octopus

Above is Eledone sp., note that it has a single row of suckers, some octopuses have a double row.

Japetella diaphna

Japetella diaphna, octopus

Japetella diaphna, above, is a deep-water octopus found from 700 - 3500 metres deep in the Northern Pacific.

It uses bioluminescence to attract mates, and broods its eggs in its arms. A fully grown adult is just 10 centimetres long.

Opisthoteuthis sp., Flapjack octopus, Pancake devilfish

Flapjack octopus, Pancake devilfish

The Flapjack octopus, Opisthoteuthis sp., above, is actually only flat in preserved specimens like this one. When alive it has a rounded body, big eyes, two small flaps on either side of its head, and is altogether really rather cute.

Octopus vulgaris, Common octopus

Octopus vulgaris, common octopus

The common octopus, Octopus vulgaris, above, has a mantle length of up to 25cm, and up to 1m including the arms. Its maximum weight is round 10kg, but most individuals are around 3kg. It is both widely studied and commercially fished with around 20,000 to 100,000 tonnes landed each year; caught mainly in octopus pots. It is found in shallow, rocky coastal waters down to 200m, more-or-less world wide in tropical and temperate waters. It is considered the most intelligent invertebrate.

The common octopus eats crabs, bivalves, gastropods, polychaetes, other cephalopods, and almost anything it can get its suckers on. It hunts at dusk, usually, and can paralyse its prey with a nerve toxin secreted in its saliva. It can change colour to blend in with the background, and then ambush passing prey. With the ends of its arms it can grope into small crevices, and it can pounce on prey trapping it under its mantle. It will also hunt buried prey by blasting the sand off with a jet of water from its siphon.

Defensive behaviour includes changing colour either to blend in or startle, and releasing an inky cloud. It is the prey for seals, larger fish, and, of course, us. Its life span is just 12 - 18 months. A female can have multiple matings, during which she collects and stores sperm packets from a number of males. Then she can use sperm from whichever packet she chooses when she decides to lay her eggs. She lays her eggs in a den attaching them to the substrate. The female lays 100,000 to 500,000 eggs which she guards, never feeding, until she dies; spending her time cleaning them and jetting water over them using her siphon. Brooding the eggs can take 4 - 5 months in colder waters.

Graneledone boreopacificus, a common deep-water (found 1 - 3km deep) octopus found in the north-east Pacific can brood her eggs for four and a half years! When brooding she uses her siphon to blow water over the eggs to keep them oxygenated, and she protects them from predation. During brooding the egg size increases, but the female does not feed, so she loses weight. She dies soon after the eggs hatch. Mantle length is around 15cm.

Octopus by A C Hilton

Strange beauty, eight-limbed and eight-handed,
Whence camest to dazzle our eyes?
With thy bosom bespangled and banded
With the hues of the seas and the skies;
Is thy home European or Asian,
O mystical monster marine?
Part molluscous and partly crustacean,
Betwixt and between.

Wast thou born to the sound of sea trumpets?
Hast thou eaten and drunk to excess
Of the sponges -- thy muffins and crumpets,
Of the seaweed -- thy mustard and cress?
Wast thou nurtured in caverns of coral,
Remote from reproof or restraint?
Art thou innocent, art thou immoral,
Swinburnian or Saint?

Lithe limbs, curling free, as a creeper
That creeps in a desolate place,
To enroll and envelop the sleeper
In a silent and stealthy embrace,
Cruel beak craning forward to bite us,
Our juices to drain and to drink,
Or to whelm us in waves of Cocytus,
Indelible ink!

O breast, that 'twere rapture to writhe on!
O arms 'twere delicious to feel
Clinging close with the crush of the Python,
When she maketh her murderous meal!
In thy eight-fold embraces enfolden,
Let our empty existence escape,
Give us death that is glorious and golden,
Crushed all out of shape!

Ah! thy red lips, lascivious and luscious,
With death in their amorous kiss,
Cling round us, and clasp us, and crush us,
With bitings of agonised bliss;
We are sick with the poison of pleasure,
Dispense us the potion of pain;
Ope thy mouth to its uttermost measure
And bite us again!