Abstract Complex internal anatomy is documented for the first time in a Neoproterozoic soft-bodied invertebrate. New data suggests that Ventogyru s, originally described as a sessile, boat-shaped form belonging to the enigmatic Neoproterozoic group Petalonamae, is actually composed of three, identical modules, arranged around an axial rod. Each module has one longitudinal and numerous transverse septa, which delimit chambers of decreasing size from one end to the other. Three distinct longitudinal channels with alternating lateral branches make up an internal network, perhaps a circulatory system. Ventogyrus is a most unusual form, particularly in the quality of its three dimensional preservation of a complex internal structure and a three-fold symmetry, a symmetry shared by many Ediacarans.