The beauty of having eight arms is that you have a wide selection of limbs to use to carry out the most varied tasks, especially if these arms have extraordinary mobility. This is the case of the octopus, which are among the smartest and “creative” animals of the world, also thanks to the fact that they have eight appendages available. Which are not all the same: a study published on Scientific Reports It shows that octopus choose which arms to use according to the task they have to carry out, and that they have a clear preference for the four front.
Arms, not tentacles. First of all: yes, we are writing “arms” and not “tentacles”. The latter are structures that have prevasile but also tactile function, and have suction cups only in the terminal part. The arms, on the other hand, like those of the octopus, are covered with suction cups throughout their length, and mainly serve to move or manipulate objects. Those of the octopus, therefore they are arms, and are composed of four separate muscle groups and distributed around a central nerve.
Muscles. This muscle “abundance” means that the arms of the octopus are extremely versatile, and that they can move and deform with a very high degree of freedom. The Florida Atlantic University team that conducted the study tried to understand how high, analyzing a series of short videos in which you can see several octopus (mostly common octopus, Octopus vulgaris) who perform actions of all kinds, from the movement to the manipulation of objects.
You prefer them. The possible combinations of movement and deformation to which octopus can submit their arms have been associated with a total of 15 different behaviors. Each arm, revealed the analysis, can perform a great variety of actions (lengthening, shortening, rolling …), without distinctions of position: all eight arms can, in theory, do the same things. In practice, however, the octopus choose which to use to do what, and have a strong preference for the four front arms, used in 64% of cases against 36% of the rear ones.
Each arm makes history in itself. There are also differences in the use of the two “sets” of arms: while the front ones are used for the exploration of the surrounding environment, the rear ones are mainly used to move. In short, the eight arms of the octopus have different tasks, something that we have so far seen only in primates, rodents and some fish.
According to the authors of the study, among other things, to understand how the arms of the octopus move could inspire the creation of very versatile mechanical arts and which work according to the same principles.