FRÚSTULA or FRÚSTULO, hard and porous cell wall of the outer layer, or teak, of diatoms or algae that constitute phytoplankton in the most superficial parts of the oceans, and that require winds and currents not to sink since they are denser than water. The frutula is composed almost entirely of silica (hydrated silica oxide) from silicic acid, and coated with a layer of organic matter, originally called pectin, a fiber much more prevalent in the cell wall of plants. This layer is actually composed of several types of polysaccharides. The frutula is usually composed of two overlapping sections or leaflets. The upper leaflet is called the epitheque and is slightly larger and overlaps with the lower leaflet, the mortgage. The junction between the two leaflets is supported by silica bands, called waist bands, which hold the two leaflets together. These bald spots are fundamental in the reproduction process, when you are bald they expand to form two new leaflets. When the cell divides, each daughter cell maintains one half of the original cell. That is, a "daughter" cell is the same size as the "mother" cell (epitheque and new mortgage) while in the other the old mortgage becomes the new epitheque in the smallest daughter cell and it will be this one that generates its new mortgage.