The stalk (spasmoneme) of the V. convallaria protozoan contracts via release of calcium ions.
"A scum-dwelling pond microbe is the inspiration for minute springs that bioengineers hope will operate tomorrow's miniaturised devices.
"Danielle France at the Massachusetts Institute of Technology is studying a protozoan called Vorticella convallaria, which can attach itself to rocks, lily pads and even other creatures in the plankton using a stalk called a spasmoneme. When the protozoan is disturbed, the spasmoneme contracts abruptly, like a stretched telephone lead springing back into a coiled shape. 'We think that it operates on stored energy,' says France…France told the American Society for Cell Biology meeting in San Francisco [in 2005] about experiments in which she spun Vorticella cells on a revolving microscope stage, exposing them to accelerations of 10,000g. Even working against the colossal resulting forces the cells could still contract their spasmonemes. The researchers calculate that a contracting spasmoneme exerts a force of at least 300 nanonewtons. That might not sound like much, but France says that, for its size, Vorticella's spasmoneme is more powerful than a car engine.
"The mighty nanospring is triggered by the release of calcium ions from the cell. The spasmoneme contains six proteins from a family called the centrins. By using antibodies to disable each centrin in turn, France and her colleagues have identified one, called centrin 5, that seems especially responsive to the calcium signal." (Aldhous 2005:12)
Learn more about this functional adaptation.