Diatoms Computerenhanced engraving of assorted species of diatom Diatoms are a group of single celled algae The two main morphological types of diatom are represented here pennate rodshaped and centric rounded A characteristic feature of diatoms is their intricately patterned glasslike cell wall or frustule The frustule consists of two halves which fit together like the lid and bottom of a box It is often decorated with rows of tiny holes known as striae Diatoms form an important part of the floating plankton in the marine and freshwater food chains Engraving taken from Ernst Haeckels famous treatise Art Forms of Nature