Visual system of marine annelids offers insights into the evolution of eyes
Larvae of the marine bristle worm Platynereis dumerilii orient themselves using light. Early in their development, these larvae swim towards the light to use surface currents for their dispersal. Older larvae turn away from the light and swim to the sea floor where they develop into adult worms. Scientists of the Max Planck Institute for Developmental Biology in Tübingen have discovered that this change in the behavioural response to light is coupled to different neuronal systems underlying the eyes. The scientists have reconstructed the first neuronal map of a visual system, from the input of the light stimulus up to the behavioural reaction - the directional turning of the swimming larva. Using this neuronal map, the biologists can glimpse the evolution of vision.