pennate diatom colony (Asterionella sp.), SEM

Coloured scanning electron micrograph (SEM) of fresh water pennate diatom colony (Asterionella sp.). Asterionella are planktonic fresh water diatoms found worldwide. The cells are joined at the broadest apex by mucilage pads to form stellate or spiral colonies. Some populations are particularly susceptible to chytrid infestations. This genus is a biological indicator of hard water. The body or frustule of each pennate cell in the colony is composed of two halves which fit tightly together. The cell walls contain silica dioxide (glass) which are preserved in deposits known as diatomaceous earth. Diatoms represent about 25% of the plant biomass in the world. These microscopic unicellular plants are important biomass and oxygen producers. Magnification: x140 when shortest axis printed at 25 millimetres.