Worms Eyes: Can Worms See?

Can worms see? And if so, how is this possible if they don’t have eyes (at least in the everyday sense of the term “eyes”)? As anyone who has spent time digging around in the mud knows, worms are simple creatures, relatively speaking. They are basically tubes with a simple digestive system and a closed circulatory system. They only have two main vessels that are as long as their body. Okay, you get the picture – they’re not that complicated. Yet, despite their obvious simplicity, they are capable of directing themselves, of moving around in the world with some notion of where they are moving. And this is what makes the question we began with interesting: if worms are so simple, they surely don’t have organs so complicated as eyes, but they are still able to move around as if they have eyes – what’s the deal?

As it turns out, the answer to the above riddle involves the definition of “eyes,” and if the definition is sufficiently inclusive, it can be properly said that worms have eyes, which explains why they are able to move around in the fashion that they do.

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Although some types of worms are blind, others, like flatworms, have what are called “pigment spot ocelli” (the singular form of “ocelli” is “ocellus,” derived from the Latin word for eye, “oculus” – who said the humanities and sciences don’t blend together?). Other creatures that have single spot ocelli include jellyfish and sea stars. In these very basic eyes, pigment is randomly distributed, making the eyes appear as red or black. There is no more advanced structure, like a cornea or lens, in the simple eyes that worms have. Within the ocelli, there are only a few light sensitive cells. For this reason, worms can only detect light that is in front of them.

As you can see (no pun intended), the eyes that some types of worms have are extremely simple, so much so that they can only faintly perceive light. However, this is evidently enough to give them a sense of direction, which explains why worms seem to “know” where they are going, as it were. To be sure, worm eyes are very primitive – in fact, it’s hard to imagine that a few light sensitive cells can be called by the same name as, say, the complicated organs that allow raptures to hunt their prey at night – but they are eyes just the same.

To conclude, worms can see with their eyes, if by “see” you mean “perceive light,” and by “eyes” you mean “a few cells that are sensitive to light.”

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