Fragilaria
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| Lyngbye |
Fragilaria (lat. Fragilis 'fragile') is a genus of diatoms (Bacillariophyta) with around 100 species that occur in freshwater and seawater.
features
The cells of Fragilaria are arranged in flat, unbranched bands, which are often twisted in their longitudinal axis. The individual cells have the typical diatom shell consisting of two counters. This is rectangular when viewed from the side and rod-shaped when viewed from the shell. The cells have a central nucleus and two plastids that lie under the shell and are golden brown thanks to fucoxanthin . The plastids contain several pyrenoids . Some species have multiple, disc-shaped plastids. Since the shells in the bands are always connected to the shell surfaces, the side view is practically always visible. The size is 5 to 170 micrometers.
Asexual reproduction occurs through the typical division of the diatoms into two parts, which leads to the elongation of the ligament. The tape can also break. The formation of permanent spores is known, but it is not known whether they are formed through sexual reproduction.
The variability of the genus results from different cell sizes, different length to width ratios of the cells in side view and the shape of the cells in shell view.
Occurrence
Fragilaria is a common genus in plankton and in the sediments of stagnant, oligotrophic to eutrophic waters. Mass developments often occur in summer. They are less common in rivers and streams.
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. 244.