First evidence that brittle stars may 'see' with their skin

Scientists have discovered the first evidence that brittle stars living in vibrant coral reefs use thousands of light sensors to navigate their way through their complex environments.

The international team, led by researchers at Oxford University Museum of Natural History, investigated the brittle star Ophiocoma wendtii, a relative to sea stars and sea urchins, which lives in the bright and colourful reefs of the Caribbean Sea. Their findings are published in the Proceedings of the Royal Society B today.

This particular brittle star first captured scientific attention more than 30 years ago thanks to striking light-responsive behaviours such as dramatic colour changes between day and night, a very strong aversion to light, and rapid shelter-seeking when exposed - all achieved without any eyes.

An enormous number of microscopic crystal bumps were discovered over the tops of the animal's arms, and for decades it has been suggested that these bumps might act as 'microlenses' in a visual system. These microlenses could be responsible for O. wendtii's incredible abilities, but no actual sensors had ever been found.

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Credit: Lauren Sumner-Rooney

Specimen of the brittle star Ophiocoma wendtii.

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Brittle stars are echinoderms, (which means spiny skin) and are usually found in the coral reefs and shallow waters almost everywhere on earth. Brittle stars have over 2,000 different species. They are closely related to the sea star and the basket star.

Like most sea stars, the brittle star has amazing regeneration capabilities. If a brittle star gets one of its arms bitten off it can regenerate a new arm. Some stars can survive with only one arm left intact, and regenerate the rest of the body.

 

Brittle stars spawning.

 

Middle Valley location (2400m below sea level), the ROPOS pilot focused his camera on a scuffle over a dead shrimp.

Ophiuroids, better known as brittle stars demonstrate their speed, agility and skill in limb-to-limb combat.