The adjective cephalopod It is used in the field of zoology to qualify a marine mollusk which has a bag with an opening, through which its head . In cephalopods, the head clearly differs from the body and is surrounded by tentacles with suction cups .
It is possible to recognize about seven hundred species of these invertebrate animals that belong to all the cephalopods. Among them we can name the squid and the octopus .
Beyond the differences between species , cephalopods share the particularity of having an organ known as foot by his head. The foot is divided into a variable number of tentacles.
In cephalopods the shell Usually disappears, becomes internal or shrinks. Another particularity of cephalopods is that they have chromatophores , cells They are in their mantle and allows them to modify their color to achieve mimicry with their surroundings and communicate with other individuals of the same species.
The secretion of ink and a body Very flexible are other properties that cephalopods have, in this case in order to hide from their predators. To hunt, these animals appeal to highly developed eyes that grant them night vision.
It is important to mention that many cephalopods are part of the diet of human being . He Galician octopus For example, it is a very popular dish that presents octopus meat with olive oil, salt and paprika. Squids, meanwhile, can be eaten fried, battered, stewed and in other ways. Interestingly, there was a time when these animals were at the top of the trophic chains of the sea.
Evolution of the cephalopods
The separation between the cephalopods and the other mollusks took place approximately 500 million years ago , when the first mollusks appeared that had the ability to fill some parts of their shell with gas to float. At present, certain species of cephalopods retain this ability, and at the time gave them the possibility to go beyond the background from the sea, where until then they were without another option, and thus access new trophic routes closer to the surface.
According to the most recent discoveries about its evolution, it is estimated that the origin of cephalopods is much earlier than previously believed. The former, who still inhabited areas near the coast, had to accept a movement towards the interior of the sea by more advanced living beings, such as marine reptiles and fish.
Another obstacle that the first cephalopods had to face was the impossibility of descending to the seabed from the surface, because their shell did not support the Pressure . As generations with smaller shells emerged, it was possible to get closer and closer to the bottom, which in turn had a positive impact on their diet.
As expected, the natural selection He leaned in favor of the latter. With the passage of time, the shell of the cephalopods decreased until it became internal or disappeared. Around 470 million years ago, the choleoids appeared (a subclass of cephalopod mollusks that currently include octopus, squid and cuttlefish, among others), and there were still some cephalopods that have already become extinct.
In accordance with the theory of the meteorite that hit our planet 65 million years ago , much of the cephalopods became extinct at that time. Ammonites are a clear example of mollusks that ceased to exist at the time. The only survivors were the nautiloideos and the coleoideos.
