Melanocyrillium is a Precambrian genus of vesicle-shaped (or vase-shaped) microfossils of uncertain affinity found in the Grand Canyon Supergroup and Togari Group of Tasmania. M. hexodiadema has been described as a "probable lobose amoeba or animal".
Melanocyrillium microfossils are characterised by a hollow, vesicle- or vase-shaped morphology, sometimes exhibiting lobed or ornamented margins. The fossils are preserved as organic-walled microstructures typical of Precambrian acritarch-like assemblages.