In Wiwaxia corrugata specimens that are between 2-8mm in length are called infants. The sclerites (plates) are fairly simple, with 5-7 ridges per sclerite. The ‘infant’ Wiwaxia does not possess any spines (Smith and Lane 2014). Specimens that are between 8-16mm in length are called juveniles. Juveniles start to develop overlapping sclerites, with each sclerite bearing 5-12 ridges. Dorsal spines start to form at this stage, but remain relatively narrow. By the time Wiwaxia has reached over 25mm in length, it is considered an adult. At this point, more sclerites have developed forming an armor-plated shield on the back. The spines are thicker and the number of ridges per sclerite has increased, ranging from 9-12 (Smith and Lane 2014). New sclerites grow once the old ones have been shed (Morris 1985; Smith and Lane 2014).
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