Molluscs are the second most diverse animal phylum. Their success in terrestrial, marine, and freshwater environments can be partially attributed to their ability to secrete a variety of biomineralized structures in the forms of shells and sclerites. Sclerites are calcium carbonate scales and spicules found in the clade Aculifera (Polyplacophora and Aplacophora). The homology of sclerites to shells in other molluscs (Conchifera) is unknown. Transcriptomic and proteomic approaches have provided insight into the genes and proteins responsible for patterning the shells of conchiferan molluscs. With no studies addressing biomineralization within Aplacophora, investigation into the proteome and development of sclerites is needed in order to make inferences about the evolutionary origins of dermal mineralized structures within Mollusca. In order to investigate the proteins involved in aplacophoran mineralization, sclerites will be collected from large-bodied species for shotgun proteomics using high performance liquid chromatography and MALDI-TOF mass spectrometry. This work will be the first proteomic analysis of aplacophoran sclerites, allowing us to make comparisons to what is known of the proteome of conchiferan shells. Additionally, in situ hybridization will be conducted in the solenogaster species Wirenia argentea in order to observe expression patters of genes encoding proteins of interest in the developing larvae. We will investigate genes with interesting properties that are identified in our proteomic work as well as genes known to be expressed during shell development such as engrailed, pif, hox1. This work will shed light on the formation of sclerites and their homology to conchiferan shells.