The same with a variety of snails, shellfish and slugs, octopuses belong to mollusks. In the traditional teaching materials of Zoology, people arranged all kinds of animals in accordance with the hypothetical evolutionary ladder sequence. And the human finally come into being. Mollusks are even in the front row of the silly sea cucumbers. People seem to forget that octopuses have the same long evolutionary history with human.
700 million years ago, our ancestors parted ways with the ancestors of octopus, taking a different evolutionary path. After a long evolution, cephalopod mollusks represented by octopus, (also including squid, cuttlefish and nautilus) quickly became a marine predator with fast speed. At the same time, they have evolved complex nervous system. Octopus not only has a brain of 500 million neurons in it (most of the snails' brains only have tens of thousands of neurons while the mouse has less than one million neurons), but also has a different distributed human neural structures. That is to say, its chain of command is not concentrated in the brain. Each one in its eight tentacles has its own separate control center. The eyes of cephalopods are also the most complicated among all invertebrates and most closest to the human eyes. Giant squid's eyeball diameter reaches 25 cm or even more. That is the largest among extant animals.
Unfortunately, many scientists’ studies have shown that although some types of octopuses, such as sand octopus can identify some of the colors, but usually the common octopuses are all color blindness. Even so, the common octopuses still can identify the size of graphics, point of view, especially in texture and gray. What’s more, the scientists also found that octopuses had the ability to distinguish polarized light and made use of the reflected polarized light by fish to locate their point of information. Therefore, it is difficult to understand what kind of world is in octopuses’ eyes. In any case, they can get enough information to identify things.