 Orthrozanclus <unk> ( " Dawn scythe with bristling hair " ) was discovered in 2006 and formally described in 2007 . This animal had a soft , unarmored underside , but the upward @-@ facing surfaces were armored by : a small shell , near the front end ; three zones of armor plates , which fitted close to the body and one of which ran all the way round the animal ; 16 to 20 long , upwards @-@ curving spines on each side of the body . The arrangement of Orthrozanclus ′ armor plates is very similar to that of its Burgess Shale contemporary Wiwaxia . Its shell is very similar to one of the two Burgess Shale shell types labelled <unk> ; the forward shell of halkieriids , most fossils of which are dated to the Early Cambrian ; and those of other Early Cambrian fossils such as <unk> and <unk> . These similarities suggest that Orthrozanclus was an intermediate form between Wiwaxia and the <unk> and that all three of these taxa formed a clade , in other words a group that consists of a common ancestor and all of its descendants . So Orthrozanclus was also drawn into the complex debate about whether Wiwaxia is more closely related to molluscs or to polychaete worms . 
