- Our Town
A nerdy mollusk with more brains than hearts
What would you do with nine “brains”? Well, if you had an 8-metre arm span, like a real Giant Pacific Octopus, Enteroctopus dofleini, and weighed 180 kg, you would need one “brain” or ganglion to control each arm and one brain in your head to keep it altogether. Indeed all octopuses, not octopi, of which there are 300 species, have nine “brains”. The average Giant Pacific Octopus weighs just 15 kg, is 90% muscle, and has three hearts: two to pump blood to its gills and one to pump blood to the body. These hyperactive aristocrats need multiple hearts; hemocyanin is their blue blood pigment, which is more efficient in carrying oxygen at low temperatures.
Octopuses are cephalopod mollusks – cephalopod means “head” (=cephalos) and “foot” (=pod), referring to the modification through evolution of the head and foot of their shelled-ancestors. Their closest relatives are squids, which have an internal shell called the pen; more distant relatives are the clams and snails. Octopuses are shell-less, and so the only obvious mollusk feature is their toothed tongue or radula, similar to the tongue of snails. Indeed, without a shell, the octopus is so flexible that a 15-kg one can squeeze through a 5-cm hole.
Snails use their tongue to scrape food off surfaces, but the octopus uses its arms to catch crabs, clams, squid, fish, small sharks, and even other octopuses. It then uses a parrot-like beak to break or crack shells and a venomous saliva to help kill its prey. The venom of Australia’s blue-ringed octopus is deadly to humans but our local octopus is not known to be harmful. The radula is then used to clean the meat out of the shells, which are then piled in middens outside the den.
Octopuses, which may be the most intelligent invertebrate, are reputed to recognize their human keepers, and they can learn to run mazes and pull corks out of bottles to get a shrimp. This level of intelligence makes them the only invertebrate for which scientists must have approval from an animal care committee before they do their research.
The Giant Pacific Octopus lives from three to five years. They only mate once, and the over 50,000-100,000 eggs are cared for by the female who dies soon after the young hatch. While we don’t know much about the health of octopus populations, it is believed that this high fecundity makes them resilient to fishing pressure.
Denis Lynn is a Professor Emeritus in Integrative Biology, University of Guelph, and an Adjunct Professor in Zoology, University of British Columbia. He taught various courses in biology during his 32-year career and still researches his favourite wee beasties, the ciliated protozoa.