An earthstar consist of a soft spore sac and an outer shell which splits into a star shape and then curls under. The spore sac has an opening at the top through which powder (huge numbers of spores) can be seen to puff when the sac is touched. For a more detailed description see Canberra Naturemap.
The species shown here is fairly common in the park, although I have never seen one with a "star" larger than about 30mm across, and according to Fuhrer it should be 70 to 100mm across.