Scientists from the University of Melbourne, University of Brussels, and Museum Victoria say that all octopuses and cuttlefish, and some squid are venomous.

The researchers say that their study suggests that they all share a common, ancient venomous ancestor and highlights new avenues for drug discovery.

Dr Bryan Fry from the Department of Biochemistry at the Bio21 Institute, University of Melbourne, revealed that while the blue-ringed octopus species remain the only group that aredangerous to humans, the other species have been quietly using their venom for predation, such as paralysing a clam into opening its shell.

"Venoms are toxic proteins with specialised functions such as paralysing the nervous system" he said.

"We hope that by understanding the structure and mode of action of venom proteins we can benefit drug design for a range of conditions such as pain management, allergies and cancer," he added.

Scientists have examined many creatures for years as a basis for drug development. However, octopuses, cuttlefish and squid remain an untapped resource.

Fry now says that their venom may represent a unique class of compounds.

For the study, his team obtained tissue samples from cephalopods ranging from Hong Kong, the Coral Sea, the Great Barrier Reef and Antarctica.

Analysing the genes for venom production from the different species, the researchers found that a venomous ancestor produced one set of venom proteins, but over time additional proteins were added to the chemical arsenal.

They say that the origin of such genes also sheds light on the fundamentals of evolution, presenting a prime example of convergent evolution where species independently develop similar traits.

Fry has revealed that the research team will next try to determine why very different types of venomous animals seem to consistently settle on the similar venom protein composition, and which physical or chemical properties make them predisposed to be useful as toxin.

"Not only will this allow us to understand how these animals have assembled their arsenals, but it will also allow us to better exploit them in the development of new drugs from venoms," said Fry.

"It does not seem a coincidence that some of the same protein types have been recruited for use as toxins across the animal kingdom," the researcher added.