We have investigated some of the many photonic and plasmonic properties of the diatom Coscinodiscus wailesii. We start by showing that when diatom frustules are converted to high-index magnesium silicide while maintaining their structure, they exhibit a broad (1μm - 2μm) photonic bandgap that varies in wavelength according to the position and angle of the incident light on the frustule. We then demonstrate the use of the micro and nanostructured silica diatom frustule as a low-cost, easily prepared substrate for surface-enhanced Raman spectroscopy by coating the frustule in 25 nm of silver and a monolayer of thiophenol. Some potential applications of diatoms to water quality measurements are suggested, and steps are taken to image a diatom frustule and chloroplasts simultaneously in vivo using rhodamine 19 dye and fluorescence microscopy. We propose future experiments that could ascertain whether there is any biological effect of the light filtering properties of the diatom frustule, and put forth some suggestions as to how to influence the morphology and photonic properties of the frustule via chemical contaminants in the diatom seawater growth medium.