Butterfield (2006) accepted that "Wiwaxia" and "Odontogriphus" were closely related, but argued that they were stem-group polychaetes rather than stem-group molluscs. In his opinion the feeding apparatus of these organisms, which consisted of two or at most four rows of teeth, could not perform the functions of the "belt-like" molluscan radula with their numerous tooth-rows; the different tooth-rows in both "Wiwaxia" and "Odontogriphus" tooth-rows also have noticeably different shapes, while those of molluscan radulae are produced one after the other by the same group of "factory" cells and therefore are almost identical. He also regarded lines running across the middle region of "Odontogriphus" fossils as evidence of external segmentation, since the lines are evenly spaced and run exactly at right angles to the long axis of the body. As in his earlier papers, Butterfield emphasized the similarities of internal structure between "Wiwaxia"’s sclerites and the bristles of polychaetes, and the fact that polychaetes are the only modern organisms in which some of the bristles form a covering over the back.