Bacillariophyta: Diatoms

Diatom morphology

More diatom morphology

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)

Pennales: pennate diatoms

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)

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

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