Nitzschia
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Nitzschia is a genus of diatoms (Bacillariophyta) with around 600 species that occur in fresh and marine water.
features
The representatives are single-celled, elongated diatoms. The cells have a two-counter shell, which is typical for diatoms. The shell is mostly rectangular in side view, rarely sigmoid. In the shell view it is boat-shaped or linear, and can also be slightly constricted in the middle. The cells are diamond-shaped in cross-section. The raphen run - unusual for pennate diatoms - not in the middle of the shell, but offset to the edge. The raphen of the upper and lower shell are diagonally opposite. The cells contain one or two elongated, lateral plastids , which are replaced by fucoxanthinare colored golden brown. The plastids extend from the side into both shell levels. The cells are 30 to 500 micrometers long.
Asexual reproduction occurs through the typical dichotomy of diatoms. Sexual reproduction occurs through anisogamy , with two gametes , rarely just one, being formed per cell . The cells then enlarge during the auxospore formation.
Occurrence
Nitzschia lives on various substrates in flowing and standing water, also in brackish water and sea water. Some species also live as plankton .
Heterotrophic species
As an exception within the diatoms, the genus includes a number of species that have secondarily given up the ability to photosynthesize. These “apochloritic” species are therefore dependent on organic carbon sources and their diet is heterotrophic . The apochloritic species still have plastids , but these are no longer colored green, but colorless. The species were found on rotting seaweed and algae, mostly in mangrove swamps . Although the findings suggest that the loss of photosynthetic ability occurred only once within the genus, the results are inconclusive. Purely heterotrophic diatoms are restricted to a few species of the genus Nitzschia and a single species of the related genus Hantzschia , but numerous other species are mixotrophic .
supporting documents
- Karl-Heinz Linne von Berg, Michael Melkonian u. a .: The Kosmos algae guide. The most important freshwater algae under the microscope. Kosmos, Stuttgart 2004, ISBN 3-440-09719-6 , p. 224.
Individual evidence
- ↑ Anastasiia Onyshchenko, Elizabeth C. Ruck, Teofil Nakov, Andrew J. Alverson (2019): A single loss of photosynthesis in the diatom or Bacillariales (Bacillariophyta). American Journal of Botany (early view, preprint) doi: 10.1002 / ajb2.1267
