Monterey Bay Aquarium Research Institute Marine Botany  How
Diatoms Reproduce  Diatoms can reproduce in two different modes,
sexual and asexual. They also may, but not necessarily, pass
through a seed-like phase known as the resting spore.  Asexual
Reproduction  Diatoms have a unique "shrinking division" mode of
asexual reproduction. After cell division, the two valves of the
test separate. Each forms the epivalve of a daughter cell, and
new hypovalves are secreted within each of the parent valves.
The result is one cell that is the same size as the parent cell,
and one cell that is slightly smaller. Due to the rigidity of
the test material, growth of the cell is impossible once the
test is secreted. Thus, the average diatom size gets
progressively smaller with each round of replication.  Sexual
reproduction  Very small diatoms may switch to a sexual mode of
reproduction. The sexual reproduction mode allows for growth of
the zygote to relatively large size. It is the escape hatch for
diatoms from the ever-shr