Revision of the problematic Vendian macrofossil Beltanelliformis (=Beltanelloides, Nemiana)

Two groups of Precambrian macrofossils are reexamined. Members of the first group are usually determined as Nemiana simplex Palij, 1976 and regarded as remains of animal organisms; members of the second are often determined as Beltanelloides sorichevae Sokolov, 1965 and assigned to green algae or cyanobacteria. The co-occurrence of the two groups in burials of the White Sea outcrops, the similarity in morphology, and the presence of transitional forms suggest that they could have been variants of preservation of the same extinct species. As a result of critical analysis of published data and examination of available type specimens, the species Beltanelliformis brunsae Menner, 1974, Beltanelloides podolicus A. Istchenko, 1988, Hagenetta aarensis Hahn et Pflug, 1988, Medusinites paliji Gureev, 1987, and Namamedusium wendti Zessin, 2008 are assigned to the same species. Beltanelliformis brunsae is regarded as the senior synonym. Taphonomic and comparative morphological data and the SEM study of phosphatized remains of Beltanelliformis agree with the hypothesis developed by M. Steiner of the microbial nature of these fossils. It is proposed that round colonies of B. brunsae grew in the area of extremely shallow water in Late Vendian marine basins. Beltanelliformis minutae McIlroy et al., 2005 is the second species of the same genus; it was more tolerant of changes in salinity and shows a wider stratigraphic range, while the species Nemiana bakeevi Becker, 1992 and Beltanelloides amorphus Menasova, 2003 are considered to have nothing in common with the groups and genus discussed.