With its eight tentacles, large eyes and intelligent demeanour, it has been likened to an alien form of life. Now scientists have decoded the genome of the octopus and have discovered just how different it is to other intelligent creatures both on land and sea.

The octopus may not have a backbone but when kept in captivity it is clever enough to devise ways of escaping from a fish tank. It is so intelligent that it is the only invertebrate to be given special protection under the UK law governing the licensing of animal experiments.

Yet the intelligence of the octopus evolved far earlier than that of the “higher” vertebrates and its genome holds the secrets of how this happened, according to the researchers who have sequenced the entire 2.7 billion “letters” of the octopus’s genetic code – the first genome within the cephalopod group of predatory molluscs, such as the squid, cuttlefish and nautilus.

“The octopus appears to be utterly different from all other animals, even other molluscs, with its eight prehensile arms, its large brain and its clever problem-solving capabilities,” said Clifton Ragsdale of the University of Chicago, one of the leaders of the international genome-sequencing project.

“The last British zoologist Martin Wells [grandson of H.G. Wells and renown cephalopod expert] said the octopus is an alien. In this sense, then, our study describes the first sequenced genome from an alien,” Dr Ragsdale said.