Do some animals have no eyes?

Yes, some animals do not have eyes. These animals are known as acoelomates, and they include flatworms, rotifers, and certain types of worms and mollusks. Acoelomates have a simple body plan and lack many of the organs and structures found in more complex animals, including eyes.

Instead of eyes, acoelomates use other senses to navigate their environment. For example, flatworms have light-sensitive cells that allow them to detect changes in light intensity, and rotifers have a pair of antennae that they use to sense their surroundings. Some acoelomates also have chemical receptors that allow them to detect the presence of food or predators.

The absence of eyes in acoelomates is thought to be an evolutionary adaptation that has allowed them to survive in harsh environments. Eyes are complex organs that require a lot of energy to maintain, and they can be easily damaged by environmental factors such as sunlight, dust, and water. By not having eyes, acoelomates can reduce their energy consumption and increase their chances of survival in challenging environments.