This creature doesn’t have a brain—or even a nervous system—but it can still see.
Erythropsidinium is a type of single-celled organism known as a dinoflagellate that, as the name suggests, propels itself using a tail (or flagellum). Most dinoflagellates either use photosynthesis or hunt their food by sensing vibrations around them. But Erythropsidinium doesn’t have to rely on such primitive methods. Its advanced eye, called an ocelloid, was discovered more than a century ago and has been admired since then for its sheer size; Fernando Gómez of the University of São Paulo, Brazil, told New Scientist that an ocelloid can take up an estimated one-third of its cell’s volume.
That the eye is so big raises questions about what it’s used for. The ocelloid looks somewhat like a vertebrate’s lens-like eyeball, except it’s actually a chloroplast that’s been modified for different purposes. While some scientists have posed that the ocelloid merely concentrates light to aid in detection, Gómez argues that the ocelloid is far to large for this to be a plausible hypothesis. Moreover, videos that Gómez has compiled of the Erythropsidinium show that the ocelloid can move in different directions, which he said it wouldn’t need to do if it acted as a mere photoreceptor.
Presumably, it’s hunting for food. How, then, would it catch transparent prey, like other dinoflagellates?
Here’s Michael La Page, writing for New Scientist:
The massive nucleus of dinoflagellates has an unusual property—it just happens to polarise light. So Leander’s team think that the ocelloid can detect polarised light, making the dinoflagellates that Erythropsidinium preys on stand out clearly against the background.
Getting conclusive evidence of what exactly the ocelloid can detect and how Erythropsidinium acts on this information will not be easy.
Erythropsidinium is hard to find, and no one been able to keep it alive in a lab for more than a couple of days, Leander says. That’s held up progress for decades. Gómez moved from Europe to Brazil to pursue his studies because Erythropsidinium is more common in tropical waters.
Scientists have yet to fully understand how this single-celled organism might create an image of something without a brain. But by putting together some of these pieces regarding the behavior and function of the ocelloid, they may be able to see the entire picture more clearly.