 He also doubted whether the two tooth-rows of "Odontogriphus" and "Wiwaxia" could perform all the functions of the multi-row radula – rasping, capturing scraped food, sorting it and transporting it to the gullet.In his opinion the differences between the narrower first tooth-row and slightly wider second one in both "Odontogriphus" and "Wiwaxia" were unlike those of a molluscan radula, in which the much more numerous tooth-rows are identical; instead he argued that these two rows resembled the permanent lower jaw and moltable upper jaw of modern dorvilleid polychaetes.While Butterfield agreed that the dark patches round the foot served as gills, he denied that they were similar in structure and mode of development to molluscan ctenidia.