It seems that brachiopods had simple eyes 600 million years ago. PZ Myers at Pharyngula explains how we know about them: common feature likely features of a common ancestor. Modern brachiopod larvae, even at a very early stage, show an earlier evolutionary stage: photosensitive pigment patches with no eye, no brain, and no nervous system. They drift towards a light source, which makes us think that
… light stimulation of the opsin is coupled to the activity of cilia used for motility in the outer epithelium of the embryo.
You can find out more at the Kewalo Marine Laboratory. Here’s a link to the article by Passamaneck, Furchheim, Hejnol, Martindale, & Luter: Ciliary photoreceptors in the cerebral eyes of a protostome larva.