Records of a new spongelike group in the Riphean biota

New microfossils of presumably sponge organization grade have been recorded in the Meso-Neoproterozoic boundary beds of the Riphean Lakhanda Formation (Maya River, Uchur-Maya Region, southeastern Siberia). Because of the microscopic size, they remained invisible for a long time among abundant green algae on the surface of individual acritarchs in associations with nematode-like organisms and zygotes and suspensors of fungal microfossils. The specimens were found during a reexamination of the type material of Annulusia annulata Timofeev et Hermann, 1979, fixed on biofilms. The biofilms have shown the presence of very small, abundant, colonial organisms represented by aggregations of cells tightly connected in a soft tissue structure. In morphological characters, mode of life, occurrence of spicule-like structures, symmetry of their body, with a central canal positioned at the apex and interpreted here as an osculum, they are considered to be similar to the sponges Demospongiae and Hexactinellida. The microfossils with a syncytium and collagen-fibrous network (amorphous body) resemble the sponge class Hexactinellida.