In a Marine Worm’s Eyes, the Theory of Evolution: Swim to the light…
An primitive cup photo sensitive eyeball that swims, imagine that. Wait, you don’t have to because one exists.
Four-day-old lamp shell larvae, for example, have puzzling dark spots on either side of the front end of their bodies. Recently, Carsten Lüter, a biologist at the Berlin Museum of Natural History, and his colleagues dissected the eyespots of some lamp shell larvae. They discovered that each spot was actually a pair of neurons, one for capturing light and one containing pigment. The neurons connected to a brainlike clump of neurons inside the larva.
Their anatomy suggested the spots were simple eyes. So Dr. Lüter and his colleagues contacted Dr. Passamaneck and his colleagues at the University of Hawaii, who are experts on the genes for animal photoreceptors. The Hawaii researchers discovered that, indeed, photoreceptor genes were active in the dark spots.
But to be thorough, Dr. Passamaneck checked to see if the photoreceptor genes were active at other stages. “I thought, ‘I’m just going to eliminate that possibility,’ ” he said.
Just the opposite happened. Dr. Passamaneck discovered that the genes were active much earlier, just 36 hours after fertilization, when the lamp shell embryo was merely a cup-shaped mass of a few hundred cells.
Dr. Passamaneck was baffled. “There are no neurons at that stage,” he said. Nevertheless, it was clear that the outer surface of the cup was covered with photoreceptors.
To see if the embryos were doing something with the light, Dr. Passamaneck and his colleagues put a light on one side of a dish of embryos. The lamp shell embryo is covered with tiny beating hairs, which it uses to swim in a spiral pattern. Dr. Passamaneck found that after 20 minutes, twice as many embryos would end up on the illuminated side of the dish as on the dark side.
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