BIO: Octopus vs Octopus

From the phylum of molluscs, class of cephalopods, there are many species of octopus around the world, and we generally cannot tell the difference with octopuses ...

 

Usually, we don't look for octopuses: they are the ones who often find us! Even if we should only see one in… a certain number watching you pass, certainly very intrigued to see this large animal with 4 tentacles not very skilled underwater. As with many animals, you will pass by dozens of individuals without even noticing them!

 

 

In the Mediterranean, you will be able to cross during your dives, essentially two species of octopus; but the common octopus (Octopus vulgaris) is the one you will see in almost every meeting. Day and night, from the surface, encounters with this species are common.

Far from the Big Blue, there are of course many species, but some could attract your attention ...

In Southeast Asia, divers who have explored the riches of the Lembeh Strait in particular will have come across the most surprising of species… the mimetic octopus. But let's save it for later ...

As a mollusk, the octopus has a soft body. But unlike most of them, this one has no hard parts, apart from a small beak at the mouth. It is this characteristic that allows it to go pretty much where it wants to go, even sometimes in very small cavities. Its head is located between a globular body, containing all the organs, and 8 tentacles each having two rows of suction cups. Its gills are located in the palleal cavity. A siphon allows water to come out, but also to propel the animal to move. It is in this cavity, also, that is the “ink bag” used in the event of aggression.

The great strength of octopuses, and other cephalopods, is precisely to be able to be very discreet in their environment. And they have an unstoppable weapon for that: the chromatophores! These “magic” cells of the skin, which have the capacity to deform a small bag filled with the pigments they possess, the cytoelastic sacculus. By changing the shape or size of these elements, the animal's skin changes color… It can then blend into the background by homochromy.

As I already said above, when one finds a small pile of empty shells at the entrance of a hole, it is because Mr. Octopus is not far! Bivalves that live buried in the sand are a delicacy he appreciates. But its favorite food remains crustaceans, mainly crabs. To hunt them, he can put himself on the lookout and pounce on a passing prey. It then uses its “parrot” beak to inject a venom, which will make the flesh liquid, and suck it up.

It is certainly the first fruits of the feast that I had the opportunity to film when during a dive near Marseille, I came across a fight between two individuals, one of whom was very white… There had a good chance it was a female, exhausted after venting her eggs until they hatched. In most cases the female dies right after… but the eggs have survived and the young are born… The goal is achieved. Sometimes, and even often, the life of some begins with the death of others ...

These animals have long interested scientists, and are considered today to be the most evolved invertebrates.

Some species of small Asian octopus have taken to the habit of taking refuge inside the shells of a bivalve, or even of making a "false shell shell" using two pieces of coconut. that they assemble!… They have even developed a way of moving with their coconut… An easy operation for the “nerd” of molluscs!

It was only in the 90s that the most formidable octopus was discovered. Its habitat: a sandy-muddy bottom of volcanic origin, found in particular in the Lembeh Strait in Indonesia. This is where the one who was baptized mimetic octopus lives (Thaumoctopus mimicus). It is not easy to move around, in order to find shelter or food, on this flat and homogeneous bottom. And given the species that roam ... it would be suicide!

Anthony LEYDET

on scuba people