The strange eye under the sea

Sea urchins use spikes on their bodies to observe their surroundings, Italian biologists said.

Scientists know that sea urchins (also known as prickly urchins), one of the invertebrate groups, have no eyes or any organs like eyes. However, they still respond to light. So many people want to know how they look.

A previous study found that purple sea urchins on the US coast of California possess many genes involved in the development of the retina.

Sea urchins in Canadian waters. Photo: National Geographic.

National Geographic said that biologist Maria Ina Arnone belongs to Anton Dohrn Animal Research Station in Italy and colleagues analyze sea urchins to learn the truth. They found two groups of cells that sense light at the top and base of the tubular spines that grow around them . Because sea urchins move with spikes, many call their spines as legs.

' We judge that sea urchin spikes have the same function as the retina ,' Arnone said. She added that some previous studies have shown that the number and location of sea urchin spikes affect their ability to 'look'.

Sea urchins are echinidea species of Echinoidea class. Their soft bodies are protected by a hard and symmetrical shell. Outside the shell there are many tubular spines. Scientists have identified about 700 species of sea urchins. They are distributed in most of the sea on the planet. Spikes of many sea urchins can reach as long as 30 cm. Some species possess poisonous spikes to defend themselves against enemies.