Diatoms belong to the Chrysophytes and are famous for their beautiful, intricately patterned cell walls.

1. The wall is made of TWO OVERLAPPING HALVES that fit like a SOAP BOX

The cell wall, called the FRUSTULE, consists of two valves:

• EPITHECA — the larger, upper half (the lid)
• HYPOTHECA — the smaller, lower half (the box)

The epitheca fits over the hypotheca exactly as the lid of a soap box fits over the box.

2. The wall is EMBEDDED WITH SILICA ($SiO_2$)

Because of this, the wall is INDESTRUCTIBLE — it does not decay. When diatoms die, the silica walls pile up on the sea or lake floor over millions of years and form large deposits called

$$\textbf{DIATOMACEOUS EARTH}$$

Uses of diatomaceous earth:

• Polishing agent
• FILTRATION of oils, syrups and sugar
• Heat and sound insulation
• Toothpaste and abrasives

Other points about diatoms:

1. They are microscopic, unicellular, photosynthetic organisms, mostly marine
2. They are the CHIEF PRODUCERS in the OCEANS — the foundation of the entire marine food chain
3. Their walls carry exquisite markings and patterns, which is why they are called the jewels of the plant world"