COATES, M.M.*; THOMPSON, S.H.; NILSSON, D.-E.: The image forming capabilities of the camera-type eyes of a box jelly, Tripedalia cystophora

Although box jellies (class Cubozoa) are traditionally thought to be simple animals they possess amazingly complex visual hardware. First described over 100 years ago (Conant, 1898), the 24 eyes on a box jelly are of two basic types: simple ocelli and lensed, camera-type eyes. The camera-type eyes are similar to those of cephalopods and vertebrates, and completely unique within the phylum Cnidaria. Conant?s description of these remarkable eyes opened many questions: Why do box jellies have such complex visual structures? How do they perform? Today these questions remain largely unanswered. To begin looking at these questions I measured the focal distance for the lens of the large camera-type eye using a modified version of the hanging drop technique (Homann, 1928). When compared to TEM sections of the eye the focal point falls behind the retina. The lens probably serves as a low pass filter, removing high frequency components of the image. What spatial information is important to box jellies? While most jellyfish are pelagic, cubozoans are neritic, living near shore often in kelp forests or mangrove swamps. I hypothesize that the large camera-type eyes of Tripedalia are well suited for the detection of the mangrove roots in their environment. If an image of a mangrove root is resolved on the retina then the motion of that image across the retina (for example as the box jelly begins to drift with the current) may also be resolved. This will aid in judging and maintaining location in the mangrove swamps, avoiding obstacles, or being swept offshore.