Diatoms
- Single-celled algae that possess a distinct nucleus (eukaryotic).
- They are represented by two major groups based on the structure and shape of the valves. These are the Centrics (Order: Biddulphiales) and the Pennates (Order: Bacillariales).
- They are most like plants in their ability to meet their nutritional needs through photosynthesis.
- The presence of chlorophyll and accessory pigments, especially fucoxanthin, give them a golden color and serves to harvest light energy from the sun.
- Cells are encased in transparent glass-like (silica) “container” called a frustule that resembles a petri-dish, with the over-lapping part called an epitheca and the lower part called a hypotheca.
- The frustules can be ornate and very beautiful, and due to the resistance of silica, they form an important part of the fossil record.
- Cells may form chains or colonies.
- Up to 100,000 species of diatoms have been recorded world-wide.
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Dinoflagellates
- Single-celled eukaryotic micro-organisms.
- They possess a distinctive nucleus where they maintain continually condensed chromosomes.
- Characteristically have two flagellae which afford them some mobility.
- Cells are covered by a theca (sheath) that can be smooth or ornamented.
- Some species migrate vertically in the water, possibly seeking nutrients, prey or refuge from damaging uv rays.
- Nearly half of known species are capable of photosynthesis (autotrophy) and possess light harvesting pigments.
- Others can survive by a variety of other nutritional modes such as an ability to absorb organic matter &/or engulf microbial prey (heterotrophy).
- Some species are capable of a combination of autotrophy and heterotrophy.
- Of the 2000 species known, about 60 species are known to produce complex toxins.
- Dinoflagellates are a very successful group, at times to the detriment of the ecosystem. When conditions are favorable, a population explosion or bloom may occur, sometimes resulting in contamination of fish and shellfish and posing a threat to human and animal health.
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