An Overview of Diatom Classification with Some Prospects.
Diatoms are silicified algae of small size. Functionally, they are single cells even though they can appear as filaments, chains, or colonies, either in the water column (phytoplankton) or attached to any single substratum (benthos). The siliceous cell wall encloses the organs of the cell and has ornamented and complex structures.
The classification system developed by Simonsen (1979) and further developed by Round et al. (1990) is currently the most commonly accepted. Diatoms commonly found in the marine plankton may be divided into the centric diatoms including three sub-orders based primarily on the shape of the cells, the polarity and the arrangement of the processes.
As algae, diatoms are protists. This means that they are eukaryotic organisms that are not specifically defined as plants, animals or fungus. Formally, they are classified under Division Chrysophyta in Class Bacillariophyceae. This Class of organism is distinguished by the presence of an inorganic cell wall that is composed of hydrated silica.
Examples of Diatom Protists. We can classify diatoms based on their morphology, or shape--specifically the shape of the silica shell. This shell is called the frustule, and the shape of the.
According to the recent classification, diatoms are divided into three classes: centric diatoms (Coscinodiscophyceae), pennate diatoms without a raphe (Fragilariophyceae), and pennate diatoms with a raphe (Bacillariophyceae). A raphe is a ridge where two halves of the diatoms join.
The pennate diatoms are usually radially symmetrical while the centric diatoms are generally bilaterally symmetrical (Alexopoulos, 1967). These two classes can be found in both marine and freshwater habitats, but centric diatoms are more likely found in the oceans while the pennate diatoms are predominately found in freshwater (Round, 1990).
Some molecular phylogenies indicate that the radial centric diatoms are paraphyletic with respect to a monophyletic group containing the polar centric diatoms and pennate diatoms. There is little support for monophyly or paraphyly.
A diatom is a unicellular eukaryotic alga characterized by the siliceous covering and symmetry. Diatoms are mostly aquatic, being found in fresh, brackish, and saltwater. They comprise the taxonomic class Bacillariophyceae. They may be solitary or in colonies.
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Diatoms are traditionally divided into two orders: centric diatoms (Centrales), which are radially symmetrical; pennate diatoms (Pennales), which are bilaterally symmetrical. The former are paraphyletic to the latter. A more recent classification divides the diatoms into three classes or subclasses and a number of orders: centric diatoms.
What's the difference between a pennate and a centric diatom? Unanswered Questions.. Yes, centric diatom are algae that are species that display radial symmetry. Diatoms are like clams, they.
The centric diatoms are radially symmetrical, with parts radiating out from a central point. The pennate diatoms exhibit bilateral symmetry, meaning the left and right halves are mirror images of each other.
Pennate diatoms are believed to have arisen from the polar centric diatoms (Medlin et al., 2000; Kooistra et al., 2003) and they are first found in the fossil record about 70 million years ago (Raven and Waite, 2004). The most ancient fossil records for silicified centric diatoms are about 120 million years old (Raven and Waite, 2004).
Blooms, after Close Sedimentation (settling out) The tendency for particles to settle out of the water column and come to rest at the bottom due to gravitational forces.Factors that influence the rate of sedimentation are particle size, water density and currents. sedimentation, can inhibit growth of benthic shellfish by clogging the gills (Chauvaud et al. 1998, Lorrain et al. 2000).
However, the new classification does have the virtue, relative to the Round et al. (1990) classification, that it reflects better the finding, now generally agreed and consistent with the fossil record, that diversification occurred first among diatoms with a centric valve structure, and that pennates evolved later from within one out of several or many centric clades.
Diatoms -- particularly centric diatoms -- constitute a major component of the marine phytoplankton. Per acre productivitity is not especially high in the open ocean, but because of the vast area covered by oceans, diatoms turn out out be major players in the global carbon balance.
Freshwater and Marine Diatom Analysis Accurate diatom analysis and identifications are essential to enable a robust calculation of the trophic diatom index and consequent classification of a freshwater water body and assessment of nutrient impact using DARLEQ2.