 Hence they classified both "Odontogriphus", and "Wiwaxia" with its "nearly identical" feeding apparatus, as primitive relatives of molluscs.In line with this classification they interpreted the dark patches round the foot as gill-like ctenidia, another feature of some molluscs; and the sediment that sometimes appeared in the fossils between the foot and supposed ctenidia suggested the presence of a mantle cavity.They also concluded that "Odontogriphus" was closely related to the Ediacaran animal "Kimberella", whose fossils also show signs of a fairly rigid upper "shell" made of a material that did not fossilize, and which has been interpreted as a very mollusc-like organism.