Box jellyfish seem to have eyes that peer constantly upwards, allowing them to navigate by detecting features on land.

Anders Garm at the University of Copenhagen and his colleagues made video recordings of the box jellyfish Tripedalia cystophora (pictured), which has a total of 24 eyes, made up of four types. The team found that four of these — the 'upper lens' eyes — always point straight upwards, regardless of the animals' orientation.

T. cystophora that were moved away from their preferred habitat near mangroves rapidly swam back, unless they were moved farther than 8 metres away. At this distance, surface ripples and the eyes' limited resolution would cripple the jellyfish's view of the mangrove canopy. Blocking the canopy from view with a white sheet also left the jellyfish swimming in random directions.

Credit: J. BIELECKI

Curr. Biol. doi:10.1016/j.cub.2011.03.054 (2011)