Visually guided obstacle avoidance in the box jellyfish Tripedalia cystophora and Chiropsella bronzie.

Box jellyfish, cubomedusae, possess an impressive total of 24 eyes of four morphologically different types. Two of these eye types, called the upper and lower lens eyes, are camera-type eyes with spherical fish-like lenses. Compared with other cnidarians, cubomedusae also have an elaborate behavioral repertoire, which seems to be predominantly visually guided. Still, positive phototaxis is the only behavior described so far that is likely to be correlated with the eyes. We have explored the obstacle avoidance response of the Caribbean species Tripedalia cystophora and the Australian species Chiropsella bronzie in a flow chamber. Our results show that obstacle avoidance is visually guided. Avoidance behavior is triggered when the obstacle takes up a certain angle in the visual field. The results do not allow conclusions on whether color vision is involved but the strength of the response had a tendency to follow the intensity contrast between the obstacle and the surroundings (chamber walls). In the flow chamber Tripedalia cystophora displayed a stronger obstacle avoidance response than Chiropsella bronzie since they had less contact with the obstacles. This seems to follow differences in their habitats.