Box jellyfish aren't content just to be brainless, squishy, stinging bastards. It turns out they have bewilderingly interesting vision systems, too. They have 24 eyes of four different types — including a set entirely used for peering into the sky.
The research looked at Tripedalia cystophora, which live in the roots of mangrove swamps in the Caribbean. The jellyfish must stick to a couple of square meters beneath the canopies, where their prey live, or they'll suffer starvation in the open waters.
So, how do the jellyfish stay in the right place? They use their "upper lens eyes," four eyes which can see through the water's surface and into the space above. These eyes allow them to spot the mangrove canopy at distances of at least eight meters, and navigate towards them. With the canopy obscured, they were lost. These eyes can rotate in any direction, and are suspended in the transparent tissue of the jellyfishes' bodies. As a result, the upper lens eyes are always looking straight up, regardless of the orientation of the jellyfish.
Since these creatures have no brain, this discovery offers some insight into how they handle complex tasks without any grey matter. It appears that having extremely specific sensory organs is key, and each eye type might be associated with a single behavior.
Top photograph by Daleen Loest/Shutterstock.