Question

Explain the differences between the covering (shell, frustules, or test) of a diatom, a dinoflagellate, and the covering of a coccolithophore.

Answer 1

Diatoms

• Eukaryotic single-celled algae
• Divided into 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 serve to harvest light energy from the sun
• Cells are encased in a transparent glass-like silica “container” called a frustule that resembles a petri-dish. The overlapping valve is called an epitheca and the lower valve is 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

Dinoflagellates

• Eukaryotic single-celled algae
• Many have two flagella, which allow the cells to have limited mobility
• Cells are covered by a theca (sheath) that can be smooth or ornamented
• Some species are able to migrate vertically through the water column, seeking nutrients, prey, or protection from harmful UV rays.
• Nearly half of known species are capable of photosynthesis and contain light-harvesting pigments (autotrophs)
• Some species survive by other nutritional modes, and may absorb organic matter or engulf prey (heterotrophs)
• Many species employ a combination of autotrophic and heterotrophic behaviors
• Of the 2000 known species, about 60 are able 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.