Lacking brains does not mean box jellyfish are incapable of complex visual behavior, according to a new study in Current Biology. Researchers have known for over a century that box jellyfish support an astounding two-dozen eyes. Now, they are beginning to find out how these eyes are used: four of a box jellyfish’s 24 eyes are always peering up out of the water finds the new study. These four eyes, no matter how the body is oriented, allow the jellyfish to navigate their shallow, obstacle-filled habitats, such as mangroves—and keep them from straying too far from home.
“Instead of having a single pair of general-purpose eyes like most other animals, box jellyfish have several different types of eyes used for special purposes,” Anders Garm of the University of Copenhagen explained. “This means that each individual eye type is dedicated to support only a limited number of behaviors.”
Studying the box jellyfish species, Tripedalia cystophora, a tiny (one centimeter across) Caribbean mangrove-specialist, researchers found that four of the species’ eyes serve a special purpose. These four eyes look up constantly and are able to see at least 8 meters and 180 degrees out of the water.
The researchers believe the specialized eyes are used to navigate the waters by peering up at the mangrove canopy. Why the canopy? According to the researchers the jellyfish is making sure it doesn’t stray too far from its preferred, shaded habitat where it feeds on copepods. If it heads out from the mangroves into the lagoon it faces starvation.
By moving the box jellyfish in tanks, researchers found that once out of visual range of the mangroves—and staring only at the blue sky and sunlight—the jellyfish lost all orientation, swimming randomly.
“It is a surprise that a jellyfish—an animal normally considered to be lacking both brain and advanced behavior—is able to perform visually guided navigation, which is not a trivial behavioral task,” said Garm. “This shows that the behavioral abilities of simple animals, like jellyfish, may be underestimated.”
There are just under 40 species of known box jellyfish in the world, many of which are venomous. The Tripedalia cystophora has not been evaluated by the IUCN Red List and to date has not even received its own Wikipedia page.
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