Researchers from Copenhagen found the visual organs of a starfish living at a depth of over 320 meters.
Biologists have studied the sensory system of 13 species of sea stars inhabiting the Greenland sea, and found 12 of them eye – light sensitive organs on the ends of the legs. The eyes have been found in even the most deep-sea organisms, from the depths were only the size of the pupil.
The main sensitive organs of some members of the family of echinoderms is ambulacraria legs, which are small tubular appendages with suction cups on the end. They are responsible for the sense of touch, sense of smell, there are light-sensitive organs.
The most advanced visual systems among echinoderms – sea stars: at the ends of the legs of their rays eyes are located a few hundred ommatidia, each of which, in turn, is equipped with hundreds of photoreceptors.
Eyes like that were only found in shallow-water sea stars: for example, the crown of thorns (Acanthaster planci) angle of eight degrees, which, however, allows it to effectively find coral reefs – the usual habitat and find food.
Eye photos of sea stars (left to right top to bottom – from the most shallow to the most deep on the average depth of habitat) Photo: Proceedings of the Royal Society
On depth more than 1000 meters from the surface, the sunlight no longer penetrates, so most deep sea creatures are used for orientation in space sense of smell and touch. But it is impossible with accuracy to say that sea stars that live at this depth, no eyes – and that is checked scientists under the leadership of Andres of Garm (Garm Andres) from the University of Copenhagen.
Scientists caught a few representatives of 13 species of sea stars from different depths of the Greenland sea and put them in aquariums with appropriate habitat temperatures and lighting. Ommatidia found in representatives of 12 species. The eyes of sea stars range in size and shape, but depth is correlated only to the size of the pupil – the “entry holes” ommatidium: for example, Pteraster pulvillus, living at depths of 100 to 500 meters, the size of the pupil is about 2500 square micrometers, and Hippasteria phrygiana (habitat – up to 1100 meters above the sea surface) – total 294.
The researchers tested the ability of sea stars studied by bioluminescence – the ability to transmit light signals. It found, for example, Novodinia americana – very deep (average depth is about 1150 metres) of the studied individuals. In addition, the visual system of N. americana is also one of the largest spatial resolutions.
Bioluminescence is the only source of light at great depths, where sunlight does not fall already. The presence of bioluminescence and vision in deep-sea representatives sea stars have allowed researchers to conclude that the vision they need to receive light signals from neighbors.