May 11, 2005

Box Jellyfish Has 360-Degree Vision

PARIS (AFP) -- The box jellyfish, a denizen of tropical waters, has one of the most sophisticated optical systems in the marine world, with 24 eyes to give itself all-round vision even though it lacks a brain to handle what they see, scientists have found.

Swedish researcher Dan-E Nilsson and colleagues found that the jellyfish, known for its cube-shaped head, has a cluster of eyes at each corner, making 24 in all.

Sixteen of the eyes are mere "pigment pits" that collect light, but the other eight have tiny lenses that are just one-tenth of a millimetre (0.004 of an inch) wide and surprisingly complex.

The position of the retinas and the lack of a brain -- the jellyfish has a diffuse network of nerves rather than a central nervous system -- means it is unlikely that the eight camera-type eyes can focus on fine details.

But that disadvantage is probably compensated by the positioning of the eyes and the refracted light provided by the lenses.

Put together, they enable the jellyfish to get a broad view all the way around its head, thus helping it to navigate in a crowded coastal environment, the scientists suggest.

The box jellyfish has trailing tentacles two to three metres (6.5 to 10 feet) long that can pack a lethal sting for swimmers. It feeds on small fish and crustaceans.

The study appears on Thursday in Nature, the British weekly science journal.