Box jellyfish have it over the rest of the jellyfish world—they have true eyes, featuring corneas, lenses and retinas. They have a more sophisticated nervous system too. They still don’t have a real brain, but those eyes enable them to actively hunt prey. Other jellyfish just drift and hope. Well, not really hope, because you can’t do that without a brain.
Anyway, it’s been long known that box jellies had eyes, 24 in fact, of four different types. But now researchers have found that four of those eyes just look up, and out of the water. The work appears in the journal Current Biology. [Anders Garm, Magnus Oskarsson and Dan-Eric Nilsson, "Box Jellyfish Use Terrestrial Visual Cues for Navigation"]
The studied jellies live in mangrove swamps and the studied eyes are always aimed at the tree canopy. By tracking the canopy the jellies can navigate to their preferred spots—where their favorite food, small crustaceans called copepods, are plentiful.
Their various eyes show that the jellies evolved a clever strategy. Rather than a single set of peepers that collect info for processing by a big brain, box jellies have different eye types responsible for informing different behaviors, with no brains. More evidence that it can be a mistake to overthink a problem.
[The above text is an exact transcript of this podcast.]