(diatoms) A division of unicellular or colonial nonflagellate * algae having delicately sculptured silica cell walls divided into two overlapping halves (see frustule). Asexual reproduction is by fission and * auxospore formation. There are two classes, the radially symmetrical or centric diatoms and the bilaterally symmetrical or pennate diatoms. The cell walls are extremely resistant to decay and form deep deposits of diatomaceous earth or kieselguhr in lake and ocean beds. Diatoms are sometimes considered as a class, the Bacillari-ophyceae, of the division * Chrysophyta. |
