Cloudinia are characteristic of the so-called 'Small Shelly Fauna' in the final Neoproterozoic period, called the Tommotian, and disappeared in the extinction event that marks the Cambrian boundary, most recently dated 542mya. The extinctions (which didn't affect microbes, however) are connected with the worldwide glaciation often referred to as 'Snowball Earth' and set the stage for the Cambrian explosion of life-forms.