A single celled organism called Erythropsidinium has been reported to have a tiny eye. This organism is not a simple bacteria sort of cell but is a eukaryote. It is single celled but has the kind of cell that is found in multicelled organisms like us. It is not a bag of chemicals but is highly organized with a nucleus and organelles. Among the organelles is a little eye and a little harpoon – ‘all the better to hunt with, my dear’. The eye (called an ocelloid) is like a camera with a lens and pigment responders; while the harpoon is a piston that can elongate 20 or so times in length very quickly and has a poison tip. The prey is transparent but has a nucleus that polarizes light and it is the polarized light that the ocelloid detects. This results in the harpoon being aimed in the direction of the prey before it is fired.
That sounds like a link between a sensory organelle and a motor organelle. As far as I can see, it is not known how the linking mechanism works but in a single celled organism the link has to be relatively simple (a mechanical or chemical molecular event or short chain of events). This is like a tiny nervous system but without the nerves. There is a sensor and an actor and in a nervous system there would be a web of inter-neurons that that connected the two and allowed activity to be appropriate to the situation. What ever the link is in Erythropsidinium, it does allow the steering of the harpoon to an effective direction. The cell can move the ocelloid and the harpoon. Are they physically tied together? Or is there more information processing than just a ‘fire’ signal?
This raises an interesting question. Can we say that this organism is aware? If the ability to sense and to act is found coordinated within a single cell – can that cell be said to be aware of its actions and its environment? And if it is aware, is it conscious in some simple way? That would raise the question of whether complexity is a requirement for consciousness. These are semantic arguments, all about how words are defined and not about how the world works.