Researchers have determined the mechanism by which the world's simplest vision system works. A team of biologists spent a decade studying the larvae of the marine rag-worm Platynereis, a tiny creature with just two cells that respond to light and direct the worm to swim towards it. The rag-worm and other zooplankton like krill
drift in the ocean's water columns, swimming up from the depths towards the light in order to graze on marine plants called phytoplankton near the surface. This movement, called phototaxis, is the biggest biomass displacement in the world [AFP].
The rag-worm has two cells that work together as "proto-eyes": one pigment cell and one light-sensitive cell.
First, the pigment cell absorbs light and casts a shadow over the photoreceptor cell. The shape of the shadow varies according to the position of the light source. The photoreceptor cell then converts this light signal into electricity, sending it ...
