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  Which Invertebrate is Considered the Most Intelligent?

27 June 1997

Octopuses, belonging to a group of mollusks called cephalopods, are among the most highly evolved invertebrates and considered by most biologists to be the most intelligent. Their central nervous system is among the largest and most complex in the invertebrate world, rivaling that of many vertebrates, including birds and fish. Their capacity to learn appears to be considerable. Just how much they can learn and how they learn are subjects of on-going interest and study by biologists and scientists.

The octopus possesses long term and short term memories, as do vertebrates. They learn to solve problems by trial and error and experience. Once it has solved a problem, an octopus remembers and can solve it and similar problems repeatedly. Experiments have shown that the octopus can learn to perform many unusual acts, such as unscrewing lids to get to food, maneuvering through simple mazes, and even distinguishing between various shapes.

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The common octopus, Octopus vulgaris, is frequently seen in oceancaves, crevices, and ledges off the North Carolina coast.


Aquarists at the NC Aquarium at Pine Knoll Shores witnessed evidence of the intelligence of these eight-armed creatures last winter when their octopus-in-residence began assisting them with their tank-cleaning chores. The daily ritual of collecting debris from the 300-gallon tank where the octopus lived became much easier for staffers when the octopus began handing them pieces that were difficult to reach! Eventually, the octopus began piling all the debris in one corner of the tank, eliminating the time-consuming clean-up process for the staff.


The eyes of an octopus are also much more developed than other invertebrate eyes; eye development rivals that of bony animals in complexity and efficiency. They are similar to vertebrate eyes in that they have a cornea, lens, and retina. They can see images, an ability that is not found in other mollusks or any other invertebrates.


Octopuses have other unique abilities which most mollusks lack. They are able to change the color of their mantle (body) so that they blend in with their surroundings. Special color cells called chromatophores expand and contract to control the pigments inside. The texture of the mantle can also change; appearing to look like rock, coral or seaweed. Octopuses are also known for their ability to release a purplish-black "ink" when threatened by a predator. This ink serves a two-fold purpose -- it hides the animal and it temporarily destroys the predator's sense of smell, allowing the octopus to make a quick getaway.


Divers off the North Carolina coast are most likely to encounter the common octopus, Octopus vulgaris. These clever cephalopods can be found in small dens or caves on the ocean floor. Spotting an octopus might be tricky though because they are shy as well as smart and may block the entrance to their dens with rocks to keep inquisitive visitors out!