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For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms (Centrales and Pennales; alternative names Biddulphiales and Bacillariales, as used e.g. in Lee, 1989). [9]
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 ...
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.
Skeletonema is a genus of diatoms in the family Skeletonemataceae. It is the type genus of its family. The genus Skeletonema was established by R. K. Greville in 1865 for a single species, S. barbadense, found in the Barbados deposit [Jung 2009]. These diatoms are photosynthetic organisms, meaning they obtain carbon dioxide from their ...
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]
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]
Diatomaceous earth is a soft, siliceous, sedimentary rock made up of microfossils in the form of the frustules (shells) of single cell diatoms.This sample consists of a mixture of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms.
Diatoms have a silica shell with radial (centric) or bilateral (pennate) symmetry Silicified frustule of a pennate diatom with two overlapping halves Guinardia delicatula , a diatom responsible for algal blooms in the North Sea and the English Channel [ 25 ]