Are the new Ediacaran Doushantuo embryo-like fossils early metazoans? A reply

Chen et al. (2014) described a suite of one-celled, Parapandorina-stage, Megaclonophycus-stage (some with dyads and tetrads), and matryoshka-stage fossils from the Doushantuo Formation, and interpreted them as representing a sequence of ontogenetic stages of the animal embryo-like fossil Megasphaera. Tang (2015) argues that the matryoshkas might have been parasites or symbionts, rather than developmental products of dyads and tetrads in Megaclonophycus-stage fossils. Assessing Tang's (2015) arguments against available evidence, we conclude that the matryoshkas likely represent an ontogenetic stage of Megasphaera. As such, they have the potential to illuminate the developmental biology, life cycle, and phylogenetic affinity of the enigmatic fossil Megasphaera.