Australia's tiny blue-ringed octopus has long had a venomous reputation—one bite can kill an adult human in minutes. But now it seems the rest of the eight-legged species' relatives are not as harmless as once thought.

According to a new study, all octopuses, cuttlefish, and some squid are venomous.

The largest known octopus species, the giant Pacific octopus, can reach sizes of more than 16 feet (5 meters) across. But the 5- to 8-inch (12.7- to 20.3-centimeter) blue-ring remains the only one dangerous to humans.

The find helps explain a long-standing mystery as to how exactly octopuses hunt and kill, said study leader Bryan Fry, a venom researcher at the University of Melbourne's Department of Biochemistry.

Scientists have known that octopuses use their beaks to drill into shelled prey, such as clams, but no one was sure just how octopuses kill their victims.

The work might also have implications for medical research, according to the study authors.

Common Ancestor

Fry and colleagues collected tissue samples from hundreds of cephalopod species during several expeditions in the waters around the Great Barrier Reef, Hong Kong, and Antarctica.

The team focused on three species found in northeastern and southern Australian seas: the blue-ringed octopus, the sand octopus, and the reef cuttlefish.

In addition to finding venom proteins, the team discovered that the venom genes from all three species seem to come from a common ancestor. Octopus venom also appears to contain similar proteins to those in other poisonous creatures such as snakes.

"It shows how little we know about the biology and physiology of these animals," Fry said.

By studying proteins from various cephalopods, the researchers hope to understand why so many different toxic creatures seem to share a similar basic venom chemistry.

Knowing more about the properties that make specific chemical brews work as toxins could aid in human drug design, the study authors say.

That's because many animal venoms have already shown promise for treating ailments such as pain, allergies, and cancer. (Related: "Toxic Snail Venoms Yielding New Painkillers, Drugs.")