|
 Diatoms
Diatoms are in the kingdom Chromista and the phylum Bacillariophyta.
The diatom is one of the most important global primary producer.
They are also among the most important aquatic micro-organisms
and because they are photosynthetic,
they are an important food source for marine organisms today.
It is unicellualr organism or aggregated in chains or starlike
groups. Cells are incased in frustules (a glass like shell that
allows light to pass through it) of silicon - dioxide and pectin.
Diatomaceous earth is a fossil deposit of diatoms. Some rocks
are formed almost entirely of fossil diatoms. In Lumpoc, Ca.
by Santa Barbara, there are many examples of diatomaceous earth
where you can find many fossiles of tropical fish in the sediment.
Some of these fossils have dated by 18 million years.
The reproduction of a diatom can be both asexual and sexual.
In asexual reproduction the cell divides into two identical daughter
cells. Valves of fustule separate and each produces a smaller
valve (one lineage keeps getting smaller) until finnaly too small
to continue the cycle. The advantage to this type of reproduction
is a rapid increase in population size when conditions are right.
In sexual reproduction the organism produces gametes (sperm
and eggs.) In some fertilazationn produces a resting stage called
an Auxospore. The advantage of this type of reproduction is increased
variation and a better chance of survival if the environment
changes.
Diatoms can be either planktonic (drifting) or benthic (on
the bottom of perhaps attached to something like a whale.)
More good sources of diatom information can be found going
to fossil
records of diatoms and the diatom
collection.
|