BBC: They say that fossilised traces of the 540-million-year-old creature are "exquisitely well preserved". By Pallab Ghosh
'The microscopic sea animal is the earliest known step on the evolutionary path that led to fish and - eventually - to humans.
'Details of the discovery from central China appear in Nature journal.
'The research team says that Saccorhytus is the most primitive example of a category of animals called "deuterostomes" which are common ancestors of a broad range of species, including vertebrates (backboned animals).
'Saccorhytus was about a millimetre in size, and is thought to have lived between grains of sand on the sea bed.'
"Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)" by Jian Han, et al here