Like its relatives the sea anemone and coral, the jellyfish looks like a no-frills animal. It has no head, no back or front, no left or right sides, no legs or fins. It has no heart. Its gut is a blind pouch rather than a tube, so its mouth must serve as its anus. Instead of a brain, it has a diffuse net of nerves.
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The Complexity of Jellyfish For all their noble antiquity, jellyfish have long been ignored or misunderstood by mainstream science, dismissed as so much mindless protoplasm with a mouth. Now, in a series of new studies, researchers have found that there is far more complexity and nuance to a jellyfish than meets the eye — or eyes.
Box jellyfish have an impressive set of 24 eyes of four different types, including eyes structurally similar to those of vertebrates and cephalopods [1,2]. However, the known visual responses are restricted to simple phototaxis, shadow responses, and object avoidance responses [3,4,5,6,7,8], and it has been a puzzle why they need such a complex set of eyes. Here we report that medusae of the box jellyfish Tripedalia cystophora are capable of visually guided navigation in mangrove swamps using terrestrial structures seen through the water surface. They detect the mangrove canopy by an eye type that is specialized to peer up through the water surface and that is suspended such that it is constantly looking straight up, irrespective of the orientation of the jellyfish. The visual information is used to navigate to the preferred habitat at the edge of mangrove lagoons.
In The Journal of Experimental Biology, Richard A. Satterlie, a marine biologist at the University of North Carolina Wilmington, recently disputed the conventional wisdom that jellyfish lack any semblance of the central nervous system that we higher vertebrates are so proud of.
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