Archive for April 29, 2011
Looking at you through Box jellyfish eyes..
Tropical-dwelling box jellyfish have a cube-shaped body, and four different types of special purpose eyes: The most primitive set detects only light levels, but another is more sophisticated and can detect the color and size of objects. The Australian box jellyfish is also deadly; each of its up to 60 tentacles carries enough toxin to kill 60 people
A set of special eyes, similar to our own, keeps venomous box jellyfish from bumping into obstacles as they swim across the ocean floor, a new study finds.
Unlike normal jellyfish, which drift in the ocean current, box jellyfish are active swimmers that can rapidly make 180-degree turns and deftly dart between objects. Scientists suspect that box jellyfish are such agile because one set of their 24 eyes detects objects that get in their way.
“Behavior-wise, they’re very different from normal jellyfish,” said study leader Anders Garm of Lund University in Sweden.
Whereas we have one set of multi-purpose eyesthat sense color, size, shape and light intensity, box jellyfish have four different types of special-purpose eyes. The most primitive set detects only light levels, but one set of eyes is more sophisticated and can detect the color and size of objects.
One of these eyes is located on the top of the cup-like structure, the other on the bottom, which provides the jellyfish with “an extreme fish-eye view, so it’s watching almost the entire underwater world,” said Garm, who will present his research at the Society of Experimental Biology’s annual meeting in Scotland.
Credit: Anders Garm/Life Science
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Are You Protected?
Sea Walnut…….
The stealthy predator Mnemiopsis leidyi, also known as the sea walnut, uses tiny hairs, called cilia, to create a current which prey don’t notice until they are sucked into its mouth region, surrounded by two large oral lobes. The sea walnut swims using fused cilia, which diffract light in many colors in this photo.
Mnemiopsis leidyi, as it’s formally called, is a ctenophore, a group of simple animals often described as jellyfish that propel themselves using tiny hairs, called cilia.
These jellyfish are native to the Atlantic Coast of the Americas, but they can be successful, even devastating, when introduced elsewhere. In the 1980s they showed up in the Black Sea, most likely transported by ships, and multiplied. Within a few years, the Black Sea’s anchovy fishery collapsed. Mnemiopsis was one of the culprits, since it both competes with the filter-feeding fish for food and also consumes anchovy eggs and larvae.
Mnemiopsis has also established itself elsewhere, including the eastern Mediterranean, the Caspian Sea, the Adriatic Sea, the Baltic Sea, parts of the North Sea, and elsewhere, according to the scientists.
