Is the brain overrated?

Preceding the Cambrian explosion by millions of years, jellyfish have a history that goes back at least 650 million years, and they were probably the first multicellular organisms to become motile. Most jellyfish have rather simple visual mechanisms that suggest their humble beginnings, but in vision one class of these creatures stands out.

The cubozoan jellyfish, a class in the phylum Cnidaria, are visually precocious and have surprisingly sophisticated ocular anatomy. While other jellyfish have primitive eyes, the cubozoans have camera style eyes, much like squid or even vertebrates, although distinct differences exist. This class of jellyfish has members that vary in size, and Tripedalia cystophora, seen on this month’s cover, is one of the smallest of the jellyfish at 10–12 mm long. In the Caribbean, this species preys upon copepods, a tiny shrimp-like zooplankton, and must rely upon its vision to keep it in the shafts of light that filter between the mangrove roots where the copepods swarm.

The approximately 14 species of cubozoans are cuboidal in shape, as their name suggests, with roughly square sides to the bell. The stinger laden tentacles extend from each of the four corners of the …