Diatoms

[75RR]

Some useful links:
http://www.ucmp.berkeley.edu/chromista/ ... phyta.html
http://westerndiatoms.colorado.edu/abou ... re_diatoms
http://academics.smcvt.edu/dfacey/Aquat ... atoms.html (An Article)
http://www.diatoms.co.uk/ad/index.htm

[actinophrys]

Another that I've found helpful:
http://craticula.ncl.ac.uk/EADiatomKey/html/index.html (for Britain and Ireland, but of course applicable to other places too)

[lukem321]

For a quick identification:
http://cfb.unh.edu/phycokey/Choices/Bac ... o_key.html

[gekko]

A very nice (large) illustrated guide useful for identification of diatoms (focusing on South Africa) [PDF] by Taylor, Harding, and Archibald; Water Research Commission, Pretoria, South Africa.
https://www.google.com/url?sa=t&rct=j&q ... WE&cad=rja