1. Bacillariophyta: Diatoms

4. Diatom morphology

5. More diatom morphology

10. Centrales: centric diatoms
Radial symmetry
Striae composed of linear punctae
May be single-celled like Cyclotella (above) or colonial: in filaments or like Tabellaria (above)

11. Pennales: pennate diatoms

12. Pennales Bilateral symmetry
Many groups possess a raphe-these are motile; some have a pseudoraphe
Many are epilithic, benthic, etc. (provides substrate for gliding
Generalization: pennate diatoms are more common in eutrophic waters, centrics in oligotrophic waters;
hence, A/C (araphidinieae : centric) index is one indicator of water quality (in lakes of low alkalinity)

14. Preparation of diatoms for microscopic observation
Ash on hotplate
Oxidize organic material
BEWARE!!!!!
30% hydrogen peroxide
Add small amount of potassium dichromate which is a catalyst

15. Characteristics Reproduction: produces auxospores
Frustules made of silica (often a limiting nutrient)
Unicellular or colonial
Form diatomaceous earth
Opal is the mineralized form of sedimented diatoms
Reproduction: produces auxospores