But at least one invertebrate, the octopus, may possess enough brainpower to alter this biological prejudice. Octopuses are mollusks, like snails, clams and oysters, but they are smarter, nimbler, more curious and more resourceful than any oyster. The central nervous system of the octopus is among the largest and most complex in the invertebrate world, rivaling that of many vertebrates, including birds and fish. How intelligent that nervous system makes the octopus is still a matter of scientific debate, however. Over the years, scientists have tested octopus intelligence by teaching captive specimens to slither through simple mazes and to tell squares from crosses.
Octopuses even learn to unscrew lids to get at food.
The most dramatic evidence for octopus intelligence came in 1992. The scientists then let untrained animals watch from adjoining tanks as their experienced confreres reached for red balls over and over. Thereafter, Fiorito and Scotto reported, most of the watchers, when offered a choice, pounced on red balls. In fact, they learned to do so more quickly than had the original group. Or so it seemed.