A fossil of one of the first life-forms has been found in China:
Saccorhytus was covered with a thin, relatively flexible skin and muscles. It probably moved around by wriggling.
This electron microscope image has inspired a Cambridge artist to create a more detailed image:
In Nature magazine Simon Conway Morris et al refer the 540 million year old specimens to the Deuterostomes, common ancestors of the vertebrates (backboned animals such as fish). Saccorhytus was about a millimetre in size, and is thought to have lived between grains of sand on the sea bed.