The evolutionary relationships of Wiwaxia have been debated since its discovery (Smith and Lane 2014). The shape and arrangement of the sclerites (plates) place it close to an extinct group of Cambrian animals called halkieriids, but Smith and Lane (2014) argues that these similarities are most likely the result of convergent evolution. However, the mode of sclerite replacement resembles that of Halkieria and Odontogriphus, suggesting the affinity of these groups to one another (Smith and Lane 2014). But, the foot of Wiwaxia has molluscan affinities, therefore placing it close to phylum Mollusca (Smith and Lane 2014). Recent embryological studies have shown that some lophotrochozoans, a group of animals that molluscs belong to, have a foot-like structure early in development. This would place Wiwaxia anywhere from the base of the lophotrochozoan tree to within Mollusca (Smith and Lane 2014). Other evidence that places Wiwaxia near the molluscan clade is the radula-like mouthparts (rasping structures of molluscs) and the structure of the sclerites (Smith and Lane 2014).
- Smith, M. R., and P. Lane. 2014. Ontogeny, morphology and taxonomy of the soft-bodied Cambrian ‘mollusc’ Wiwaxia. Palaeontology 57:215-229.
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