to the chitinous bristles (setae) that project from the bodies of modern annelids and in some genera form leaf-like scales that cover the back like roof tiles – in composition, in detailed structure, in how they were attached to the body via "follicles" and in overall appearance. Some modern annelids also develop on each side rows of longer bristles, which both Walcott and Butterfield considered similar to Wiwaxia'''s dorsal spines. including the halkieriids. Butterfield also contended that Wiwaxia's feeding apparatus, instead of being mounted in the middle of its "head", was just as likely to be mounted in two parts on the sides of the "head", an arrangement that is common in polychaetes. He went so far as to classify Wiwaxia as a member of a modern order, Phyllodocida, and pointed out that Wiwaxias lack of obvious segmentation is no barrier to this, as some modern polychaetes also show no segmentation except during development. He later noted that Wiwaxia lack some polychaete features which he would expect to be easily preserved in fossils, and therefore a stem-group annelid, in other words an evolutionary "aunt" of modern annelids. Conway Morris and Peel (1995) largely accepted Butterfield's arguments and treated Wiwaxia as an ancestor or "aunt" of the polychaetes, and said Butterfield had informed them that the microscopic structure of Wiwaxias sclerites was identical to that of the bristles of two Burgess Shale polychaetes Burgessochaeta and Canadia. Conway Morris and Peel also wrote that one specimen of Wiwaxia showed traces of a small shell, possibly a vestige left over from an earlier stage in the animal's evolution, and noted that one group of modern polychaetes also has what may be a vestigial shell. However they maintained that Wiwaxia's feeding apparatus was much more like a molluscan radula. They also argued that Wiwaxia was fairly closely related to and in fact descended from the halkieriids, as the sclerites are divided into similar groups, although those of halkieriids were much smaller and more numerous; they also said that in 1994 Butterfield had found Wiwaxia sclerites that were clearly hollow. They presented a large cladogram according to which: The earliest halkieriids were a "sister" group to the molluscs, in other words descendants of a fairly closely related common ancestor. The halkieriids which Conway Morris had found in Greenland's Sirius Passet lagerstätte were a "sister" group to brachiopods, animals whose modern forms have bivalve shells, but