||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.
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 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