Planarian flatworms (ghost flatworm) on reef aquarium glass
© Getty
Tiny worms can ‘see’ light without their eyes, or their heads. Planarians are a type of flatworm, soft-bodied creatures that lack complex organs. They have two eyes that connect to a centralised bundle of ganglia in their heads that acts as a brain, and those eyes are sensitive to ultraviolet (UV) light. In the presence of UV light, the worms use their cilia, tiny hairlike structures on their bodies, to wriggle away. However, it turns out the worms, measuring just a few millimetres long, don’t need their eyes or their brains for light detection. When researchers lopped off planarians’ heads, the worms were still capable of sensing UV light.