An Overview of Diatom Classification with Some Prospects.
Congruence between phylogenetic analysis and classification may yield a dramatic restructuring of the classification of the diatoms, and that has implications for training future diatom researchers. Key words: diatom classification, monophyly, paraphyly, history.
Valves with radial symmetry (symmetric about a point) Cells lack a raphe system and lack significant motility. Cells may possess fultoportulae (strutted processes) and rimoportulae (labiate processes) Sexual reproduction is oogamous.
The valve has either a pattern of radial symmetry or an elongated one, the distinction between centric and pinnate diatoms, and represents the basis for taxonomic classification (Round et al., 1990).
Check Out Our Diatoms Essay. Diatoms refer to the main group of algae and which are normally the most common members of phytoplankton family. Even though most diatoms are unicellular, they are also known to exist as colonies. Palaeo-sedimentary analysis refers to the way up criterion, structure or geopital indicator observed in volcanic.
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.
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.
