As you watch, the entire array suddenly zips out, expanding into a very long chain that resembles an old-fashioned carpenter's rule. After being extended for a moment, the colony slides back, either back into its original parallel array, or it keeps on until all individuals are extended out as far as they can go in the opposite direction. There are over five thousand species of diatoms. Some move, some don't. Some are circular, others are elongated, or square or rectangular or shaped like dumbbells.
Some colonies resemble jointed dominoes.
Because of the great variation of shape and the sculpturing of their shells, they have fascinated microscopists and botanists for centuries. There still are scientists who spend their lives studying these fascinating little plants with good reason, because diatoms are superb indicators of water quality. Other biologists seek new species of diatoms. The room was crowded with shelves reaching the ceiling, each shelf holding hundreds of microscope slide boxes, every one of which contained a hundred slides he had mounted or acquired. Long ago when they occasionally got bored doing whatever they were doing with diatoms, microscopists would select certain ones under a microscope, then move them about on the slide with a single human hair mounted on a wooden shaft.