A thin siliceous covering on the external valve surface. The conopeum may be slightly to distinctly elevated from the valve face and may partially or completely cover the striae and extend to the valve margin. This structure is visible only with the scanning electron microscope. Conopea have been found to contain symbiotic nitrogen-fixing cyanobacteria and are found in a number of genera, including Fallacia, Lyrella, Microcostatus, Nitzschia and Sellaphora.
Barber, H.G. and Hayworth, E.Y. (1981). Guide to the Morphology of the Diatom Frustule. Freshwater Biological Association, 112 pp.