Octopuses are among the most distinctive of all marine animals. Eight arms make it possible for the creatures to grab onto a rock or other structure while fighting, for prey or defense. One big question remained for biologists - how do the limbs of octopus not get tangled together? That question may now be answered.
If octopus were more intelligent, they might be able to keep track of where each arm is at all times and prevent tangling. However, brains in octopus are only about the size of a walnut, and are incapable of this level of processing.
Researchers in Israel carried out a series of tests on octopus to study the extents of octopus abilities. Binyamin Hochner from the Hebrew University of Jerusalem noticed that suckers attached to everything they touched, except each other. His team found that octopuses are able to deactivate suckers on their limbs.
"We show that the suckers of amputated arms never attach to octopus skin because a chemical in the skin inhibits the attachment reflex of the suckers," researchers wrote in an article detailing their study.
This chemical keeps the tentacles from sticking together, but the effect can be held back when the animal needs to grasp an object. Biologists have, so far, been unable to identify what chemical is responsible for preventing the limbs from becoming tangled together. Another unanswered question is how the animals are able to tell the difference between their own flesh and that of other members of its species.
These animals have other unusual features, including the ability to morph into the shape of other creatures. When they lose a limb, the body part grows back.
As part of their study, researchers amputated limbs off the test animals. When the octopus handled severed tentacles, they would often bring the limbs to their mouths to feed. The behavior was less common when the animals were handling their own detached body parts. Because the limbs had difficulty grabbing on to each other, octopus would occasionally grab their own severed tentacles with their beaks. Investigators called this behavior "spaghetti holding."
Octopus limbs are of particular interest to robot designers and researchers studying artificial intelligence. They are not controlled by the animal's small brain. Instead, each limb is controlled independently, using 250 million nerve cells. Even when detached from the animal, the tentacle continues to exhibit life-like behavior. Amputated arms will occasionally grasp onto food, and attempt to pass the sustenance to a mouth which is not there.
Investigation of octopus and their remarkable limbs was profiled in the journal Current Biology.
