On a submersible dive off the Bahamas, Mikhail V. Matz of the University of Texas at Austin and several colleagues were seeking big-eyed, glowing animals adapted to darkness. Yet as they cruised above the seafloor, the team was distracted by hundreds of bizarre, sediment-coated balls the size of grapes. Each sat at the end of a sinuous track in the seafloor ooze. Indeed, the balls appeared to have made the tracks; some even seemed to have rolled upslope.
The team collected specimens and identified the creatures as giant protozoans, Gromia sphaerica, each one a single large cell with an organic shell, or "test." When cleaned of sediment, the test feels like grape skin, but squishier, Matz says.
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