Natures wonders:brittle stars are light sensitive all over (Introduction)

by David Turell , Friday, January 26, 2018, 14:13 (2491 days ago) @ David Turell

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.