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> They have light sensitive cells everywhere on their bodies, but no eyes:
> 
> https://cosmosmagazine.com/biology/seeing-stars
> 
> "The brittle star Ophiocoma wendtii, shown above, is a relative of sea stars and sea urchins that lives among the bright reefs of the Caribbean Sea.
> 
> "The creatures have fascinated scientists for decades because they respond to light in striking ways – changing colour between night and day, avoiding light and seeking shelter when exposed – yet have no eyes.
> 
> "O. wendtii has an enormous number of microscopic crystal bumps over the tops of their arms, and it has been suggested that these bumps might act as ‘microlenses’ in a visual system. No actual light sensors, however, had been found.
> 
> "New research led by Lauren Sumner-Rooney of Oxford University has uncovered the real story. 
> 
> "Using specially-designed fluorescent antibodies, the researchers identified light-sensitive cells in O. wendtii for the first time – not only in the tops of the arms, but embedded in the skin across the entire body.
> 
> "It’s unclear exactly to what extent the brittle stars use the cells to “see”, but behavioural experiments indicate they are able to detect shadows from a distance."
> 
> Comment: Darwin thought vision started from light sensitive cells, but it is a giant step to actual eyes. The giant steps are seen in the Cambrian, but the actual evolutionary steps are not understood, since the eyes simply appear out of nothing.