Sea urchins are a kind of marine animals that we are familiar with, and some of them are edible. When many people observe sea urchins, they will find that although they are also animals, their body structure is different from many animals we are familiar with. In fact, sea urchins are invertebrates, compared with vertebrates, they do not have many structures, because they did not evolve similar structures in the course of evolution.
For example, sea urchins don't have eyes. Although they do not have eyes, they also have similar organs to sense their surroundings, which is the result of years of evolution in adapting sea urchins to the marine environment. For example, there are some epidermal cells in their abaxial surface, which have eye spots on them, which can be used to sense external light. In addition, they have enough photoreceptors on their spines and tube feet. In fact, in general, sea urchins are sensitive to the light around them. Of course, their eyesight is not comparable to that of humans and most other animals, but they can already meet the needs of sea urchins for life activities.
As mentioned above, sea urchins do not have eyes because of their simple body structure. But sea urchins have mouths, so they can eat. Many people have seen sea urchins feeding, and their mouths are relatively obvious at this time. When sea urchins are not feeding, their mouths are not easy to observe, but if you look carefully, you can see that there is a small white part of the surface without spines, which is the mouth of sea urchins.
