Eldonia is a soft-bodied animal of unknown affinity, known from the Fossil Ridge outcrops of the Burgess Shale, particularly in the 'Great Eldonia layer' in the Walcott Quarry. It also occurs in the Chengjiang biota. It takes the form of a round, medusoid disk (which originally led to suggestions of a jellyfish affinity) with a C-shaped gut trace. The gut is recalcitrant and can be extracted using HF acid. The organism is frequently found in association with the lobopod Microdictyon, which is presumed to have fed upon Eldonia.