OCTOPUS are not fresh water beasts (see below) - it is possible for one to mutate and exist but it is unlikely. An Iuz experiment?
Need for speed
Even if they did initially evolve a mechanism for coping with freshwater, Norman says that as they needed to outswim increasingly fast fish predators, and to become supercharged top-order predators themselves, many functions were lost. This allowed others to develop to extremes.
"Cephalopods have transparent blue, runny, copper-based blood that doesn't carry a lot of oxygen," he says.
"In order to maximise the amount of oxygen that could be carried by the hemocyanin in their blood, and to get their blood pressure high enough to pump blood to high speed muscles, they evolved three hearts," he adds. "In our bodies our hearts pump blood in one loop around the brain and in another around the body.
"Cephalopods have a heart above each gill (known as branchial hearts) as well as a central (systemic) heart that pumps blood around the body."
The structure of their complex nervous system also maximises speed and efficiency - either for prey capture or for escape from danger.
"They have complex visual senses, camouflage and signalling skills.
"The brains of cephalopods are ring shaped, and encircle the oesophagus, requiring them to pulversie their food before swallowing it," Norman explains.
Some nerve cells also control chromatophores, skin colour cells that, similar to a picture on a high definition television, can change instantly for camouflage. Other nerve cells also help them disappear in the blink of an eye when threatened.
"The squid giant axon [a giant nerve cell, not to be confused with a nerve cell from a giant squid] is the largest of any animal and controls escape behaviours," he says, adding that a single nerve cell can be 30 centimetres long, and up to 1 millimetre in diameter (the diameter of a human nerve cell is 0.1 millimetres by comparison).
"This means that the second the second the brain says 'go!' they're off. There is no delay as the message is transmitted between synapses as it is in other animals."
Dr Mark Norman is the Head of Science at Museum Victoria, Dr Norman spoke to Rachel Sullivan.
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