CHRYSOPHYTES: Chrysophytes include diatoms and golden algae (desmids). These are found both in fresh and marine water. They are microscopic and float passively (without using energy) in water currents. Most of Chrysophytes are photosynthetic. Silica is deposited in the cell wall of diatoms. The cell walls form two thin overlapping shells, which fit together as in a soapbox. During asexual reproduction, each daughter cell retains one half of the old wall and synthesizes a new half. Diatoms are normally diploid and reproduce sexually by producing gametes. Silica shells of dead diatoms are nearly indestructible and thus, get accumulated at their habitat. Such huge rock-like deposits of hard shells of diatoms constitute diatomaceous earth. Being gritty, the soil of diatomaceous earth. Being gritty, the soil of diatomaceous earth is used in polishing,  filtration of oils and syrups. Diatoms are the chief 'producers' in the ocean.