The eyes of most animal groups use one of two types of light-sensing cell — rhabdomeric or ciliary photoreceptors. Scientists had thought that ciliary photoreceptors, which include the rods and cones of the human retina, were unique to the eyes of chordates — animals with a backbone precursor. In non-chordates, this cell type had only ever been found in the brain or other body structures.
Now, Yale Passamaneck at the University of Hawaii at Manoa and his colleagues have found evidence of ciliary cells in the eyes of larvae of Terebratalia transversa, a member of an ancient group of non-chordates, by showing expression of a key ciliary gene for a light-sensitive protein in the eyes. The discovery could mean that the use of these cells to sense directional light evolved more than once.
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A changing eye on the world. Nature 471, 139 (2011). https://doi.org/10.1038/471139b
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DOI: https://doi.org/10.1038/471139b
