A species
Common octopus
Octopus vulgaris
Three hearts, blue blood and tasting arms
You and the common octopus last shared an ancestor about 580 million years ago (on 11 November, if life's history were one year).
This octopus has three hearts, blue blood and eight arms that taste and seem to think for themselves. Yet it is a mollusc, a relative of the garden snail shown beside it on the tree. Two hearts push blood through its gills, while the third sends oxygen-rich blood around the body. Its blood looks blue because it uses copper, not iron, to carry oxygen.
Each arm carries about 200 pale suckers in two rows. Special cells in those suckers let the octopus taste by touch. Each arm also has its own bundle of nerve cells, so it can feel into cracks and grab a crab without waiting for orders from the central brain.
Its skin can match the colour, pattern and roughness of its surroundings almost instantly. It is often mottled brown or grey, but can flash pale cream, dark brown or red. It creeps on its arms or squirts water through a funnel to dart away. It can grow up to about as long as a guitar and lives in warm, shallow coastal waters.
Squeezes through tiny gaps
It has no bones or shell and can squeeze through any hole larger than its hard, parrot-like beak, the only stiff part of its body.
Ink cloud escape
When found, it releases a cloud of black ink that hides it and dulls a hunter's sense of smell, making it harder to follow.
Night hunter with a stone den
It hunts mostly at night and hides by day in a den under rocks, often ringed with stones and scattered with freshly drilled shells.