The Eyes Of A Box Jellyfish Analysis

"If you ask people what animal eyes are used for, they’ll say: same thing as human eyes. But that’s not true. It’s not true at all.”

In his lab at Lund University in Sweden, Dan-Eric Nilsson is contemplating the eyes of a box jellyfish. Nilsson’s eyes, of which he has two, are ice blue and forward facing. In contrast, the box jelly boasts 24 eyes, which are dark brown and grouped into four clusters called rhopalia. Nilsson shows me a model of one in his office: It looks like a golf ball that has sprouted tumors. A flexible stalk anchors it to the jellyfish.

“When I first saw them, I didn’t believe my own eyes,” says Nilsson. “They just look weird.”

Four of the six eyes in each rhopalium are simple light-detecting slits and pits. But the

It took them another four years to discover what the upper lensed eyes do. The first big clue was a free-floating weight at the bottom of the rhopalium that ensures that the upper eye is always looking upward, even if the jellyfish swims upside down. If this eye detects dark patches, the jellyfish senses that it’s swimming beneath the mangrove canopy, where it can find the small crustaceans that it eats. If it sees only bright light, it has strayed into open water, and risks starving. With the help of its eyes, this brainless blob can find food, avoid obstacles, and survive. The box jellyfish’s eyes are part of an almost endless variation of eyes in the animal kingdom. Some see only in black and white; others perceive the full rainbow and beyond, to forms of light invisible to our eyes. Some can’t even gauge the direction of incoming light; others can spot running prey miles away. The smallest animal eyes, adorning the heads of fairy wasps, are barely bigger than an amoeba; the biggest are the size of dinner plates, and belong to gigantic squid species. The squid’s eye, like ours, works as a camera does, with a single lens focusing light onto a single retina, full of photoreceptors—cells that absorb photons and convert their energy into an electrical signal. By contrast, a fly’s compound eye

With each yearlong generation, it becomes a little thicker. It slowly curves from a sheet into a cup. It gains a crude lens, which gradually improves. Even under the most pessimistic conditions, with the eye improving by just 0.005 percent each generation, it takes just 364,000 years for the simple sheet to become a fully functioning camera-like organ. As far as evolution goes, that’s a blink of an eye. But simple eyes should not be seen as just stepping-stones along a path toward greater complexity. Those that exist today are tailored to the needs of their users. A sea star’s eyes—one on the tip of each arm—can’t see color, fine detail, or fast-moving objects; they would send an eagle crashing into a tree. Then again, a sea star isn’t trying to spot and snag a running rabbit. It merely needs to spot coral reefs—huge, immobile chunks of landscape—so it can slowly amble home. Its eyes can do that; it has no need to evolve anything better. To stick an eagle’s eye on a sea star would be an exercise in ludicrous