The long snout of the dwarf sea horse (Hippocampus zosterae; pictured) allows it to sneak up on its prey.
The creature sucks its victim into its mouth by quickly snapping its head upwards, but to do so it must get within one millimetre of its target without the prey sensing any movement of the surrounding water.
A team led by Brad Gemmell at the University of Texas at Austin used three-dimensional digital holography to track the flow of water around a sea horse as it swam towards a small crustacean. They found that the unique shape of the sea horse's head, along with its orientation, creates a zone in which water is undisturbed as the sea horse moves.
The results could be relevant for the design of microfluidic devices that need to move water with minimal disturbances.
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Stealthy sea horse uses its head. Nature 504, 11 (2013). https://doi.org/10.1038/504011e