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Diatoms are divided into two groups that are distinguished by the shape of the frustule: the centric diatoms and the pennate diatoms. Pennate diatoms are bilaterally symmetric. Each one of their valves have openings that are slits along the raphes and their shells are typically elongated parallel to these raphes. They generate cell movement ...
The diatom lineage may go back 180 to 250 million years ago (Mya). About 65 Mya, diatoms survived a mass extinction in which roughly 85% of all species perished. [6] Until 1994, the genus was known as Nitzschia, but was changed to Pseudo-nitzschia because of the ability to form chains of overlapping cells, as well as other minor morphological differences. [8]
Some pennate diatoms also exhibit a fissure along their longitudinal axis. This is known as a raphe, and is involved in gliding movements made by diatom cells; motile diatoms always possess a raphe. In terms of cell cycle , vegetative cells are diploid and undergo mitosis during normal cell division .
Medlin and co-workers erected a new class, Mediophyceae (which could be re-ranked a subclass if diatoms as a whole are ranked as a class rather than a phylum) for the "polar centric" diatoms, which they consider to be more closely related to the pennate rather than to other centric diatoms, a concept which has been followed or further adapted ...
The Coscinodiscophyceae are a class(s) of diatoms. [1] They are similar to the Centrales, a traditional, paraphyletic subdivision of the heterokont algae known as diatoms. [2] [3] [4] The order is named for the shape of the cell walls (or valves or frustules) of centric diatoms, which are circular or ellipsoid in valve view.
Structure of a centric diatom A single chain of Skeletonema costatum cells from a field sample from Long Island Sound. Cells belonging to S. costatum are single-celled but exist as long chains of about 6 to 24 cells [23] but can be up to 60 cells in length. [2]
Pseudo-nitzschia australis is a pennate diatom found in temperate and sub-tropic marine waters, such as off the coast of California and Argentina. This diatom is a Harmful Micro Algae [1] that produces toxic effects on a variety of organisms through its production of domoic acid, a neurotoxin. Toxic effects have been observed in a variety of ...
Fusulinid from the Plattsmouth Chert, Red Oak, Iowa ().Micropaleontology can be roughly divided into four areas of study on the basis of microfossil composition: (a) calcareous, as in coccoliths and foraminifera, (b) phosphatic, as in the study of some vertebrates, (c) siliceous, as in diatoms and radiolaria, or (d) organic, as in the pollen and spores studied in palynology.