Which invertebrate is considered the most intelligent?

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 ongoing interest and study by biologists and scientists.

The common octopus is frequently seen in ocean caves, crevices and ledges off the North Carolina coast.

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

Aquarists at the NC Aquarium at Pine Knoll Shores witnessed evidence of the intelligence of these eight-armed creatures recently  when their octopus-in-residence began assisting them with tank-cleaning chores. The daily ritual of collecting debris from the octopus’ 300-gallon home 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, greatly reducing the time-consuming clean-up process for staff.

The eyes of an octopus are well developed. They are similar to vertebrate eyes in that they have a cornea, lens and retina. They can see images, an ability  not found in other mollusks or any other invertebrates.

Octopuses have other unique abilities which most mollusks lack. They are able to change to blend in with their surroundings.  The texture of their body can also change, appearing to look like rock, coral or seaweed. Octopuses are also known for releasing purplish-black “ink” when threatened. The  ink serves a two-fold purpose; to hide or distract the predator and to temporarily destroy the predator’s sense of smell, allowing the octopus to make a quick getaway.