Erythropsidinium is a single-celled, cycloptic sniper
Whenever you see light, taste something spicy, or even jog down the street, you’re relying on specialized cells in your body, like blood or nerve cells. While this works great for elaborate, multi-cellular animals like us, how do single-celled organisms handle these activities? While lots of single-celled creatures are content to just drift, the dinoflagellate Erythropsidinium has managed to crank some amazing utility out of its tiny body, allowing it to become an active and purposeful hunter.
Various plankton are capable of shooting out small, stinging darts at potential prey, but it’s not a very efficient process. They don’t know where their target is exactly, instead reacting generally to vibrations. Erythropsidinium, on the other hand, appears to aim before firing, like a single-celled sniper. But to aim requires some sort of sensory input so you know where your target is, which brings us to Erythropsidinium’s first interesting specialization— a repurposing of what was most likely its ancestors’ chroloplasts.
Chroloplasts are used by plant-like plankton, including other dinoflagellates, to photosynthesize food. Erythropsidinium seems to have taken that light sensitivity and evolved it into a sensory organ, called a ocelloid. The ocelloid takes up a significant portion of the creature’s volume, making it a costly investment if it’s not serving the Erythropsidinium. Which seemed, at first, like a concern, because this Erythropsidinium’s favorite food is nearly invisible in normal light.
The leading theory on how this single-celled hunter is spotting its targets is that its ocelloid may be able to specifically detect polarised light. The fellow dinoflagellates that Erythropsidinium hunts all have large nuclei, which polarize light as it passes through them. If Erythropsidinium’s ocelloid is tailored to detecting this kind of light, the nearly invisible creatures would actually be quite distinct, with bulls-eyes on their nuclei.
A good offense and a good defense
This is not the end of this creature’s arsenal, though. To further take advantage of being able to target other animals, Erythropsidinium also has a long, extendable structure called a piston. It can quickly stretch it to full length, with enough force to possibly push a potential predatory plankton away. This hasn’t been confirmed in action yet, but if this behavior is proven, it will reinforce the notion that Erythropsidinium has a variety of visually-oriented tricks up its sleeves, all packed into one single cell.
Source: This single-celled bug has the world's most extraordinary eye by Michael Le Page, New Scientist