So far "Kimberella" fossils show no sign of a radula, the toothed chitinous "tongue" that is the diagnostic feature of modern molluscs, excluding bivalves. Since radulae are very rarely preserved in fossil molluscs, its absence does not necessarily mean that "K. quadrata" did not have one. The rocks in the immediate vicinity of "Kimberella" fossils bear scratch marks that have been compared to those made by the radulae of molluscs as they graze on microbial mats. These traces, named "Radulichnus" and "Kimberichnus", have been interpreted as circumstantial evidence for the presence of a radula. In conjunction with the univalve shell, this has been taken to indicate "Kimberella" was a mollusc or very closely related to molluscs. In 2001 and 2007 Fedonkin suggested that the feeding mechanism might be a retractable proboscis with hook-like organs at its end. "Kimberella"′s feeding apparatus appears to differ significantly from the typical mollusc radula, and this demonstrates that "Kimberella" is at best a stem-group mollusc. Notably, the scratch marks indicate that the 'teeth' were dragged towards the organism, not pushed away as in molluscs, and that the maximum impact on the sediment was when the mouthpart was furthest from the organism. The direction of grazing is also backwards, as opposed to forwards as in molluscs. Furthermore, the constant width of grooves implies stereoglossy – a trait that is very derived in molluscs. It has been argued that the shape of the feeding traces is incompatible with a radula, and that despite the molluscan body form, the lack of a radula places "Kimberella" well outside the molluscan crown group. Butterfield points out that plenty of other groups of organisms bear structures capable of making similar marks.