At http://www2.le.ac.uk/news/blog/2017-archive/january/discovery-of-new-fos… … the fossil loriciferan is so small it was thought to be fossilisable.
… It is in fact a microfossil and was discovered under the microscope whilst looking for something entirely different. Scientists from Leicester and Cambridge Universities were examining mud stone from western Canada – dating to the Cambrian epoch (half a billion years ago). Even more unusual, and upsetting for uniformitarians no doubt, is that loriciferans lack hard parts. They have no shell for example. It is entirely a soft parts organism – and therefore is not supposed to be fossilisable. Yet they were. It is thought they hid among grains of sediment on the sea floor – the assumption being that mud stones formed on sea and lake beds. However, if they were preserved as a result of being quickly buried in mud they could well have been water suspended animals and not bottom feeding ones. It all depends on how you look at mud stone formation – rapid, or prolonged (over long periods of time).