Zygnematophyceae

The body plan of Zygnematophyceae is simple, and the group appears to have gone through a secondary loss of morphological complexity. The most basal members are unicellular, but filamentous species have evolved at least five times, cell walls are composed of three layers: one outer layer consisting of mucus, a primary wall consisting of microfibrils, and an innermost layer of cellulosic microfibrils. Some species shed their primary wall and retain only the innermost layer. The cell wall may be variously decorated with striations, granules, or spines. In the Desmidiales, there are pores in the cell wall which allow the cell to extrude a layer of mucilage for protection. A new subclass called Spirogloeophycidae, represented by the species Spirogloea muscicola, was established after the unicellular subaerial algae, resembling a "gelatinous blob", was rediscovered on a rock close to a river bank near Cologne in 2006, after first being discovered in France in 1845. ==Reproduction==

The Zygnematophyceae are able to reproduce both asexually and sexually. Asexual reproduction takes place via fragmentation, cell division, akinete formation, or parthenospores. Unusually, the gametes lack flagella, and they also lack centrioles which suggest that flagella were not secondarily lost. This lack of flagella sets the Zygnematophyceae apart from nearly all groups of algae, except for red algae and cyanobacteria (also known as blue-green algae, if they are classified as such). ==Taxonomy==

The Zygnematophyceae is monophyletic. Traditionally, it has been known to contain two orders, the Zygnematales and Desmidiales. Class Zygnematophyceae • Subclass Spirogloeophycidae Melkonian, Gontcharov & Marin 2019 }} }} }} }} }} }} }} ==Habitat==

Members of the Zygnematophyceae are common in nearly all freshwater habitats, particularly filamentous genera such as Spirogyra and Mougeotia. Some Spirogyra species can tolerate disturbed habitats. On the other hand, desmids (the Desmidiales) often prefer bogs, peatlands, and lakes. ==Fossil record==

Vegetative cells of the Zygnematophyceae are fragile and usually not preserved, but the zygospores are resistant to decay and can become fossilized. The Zygnematophyceae have been recorded from at least the middle Devonian period, and before the Carboniferous period, all the major groups had diverged. Fossils of zygospores are indicators of warming spring conditions and shallow, stagnant mesotrophic habitats. ==Genomes==

The first genomes published for Zygnematophyceae were Mesotaenium endlicherianum and Spirogloea muscicola. Zygnema spp., and the Closterium peracerosum–strigosum–littorale complex. Furthermore, the gene models of Mesotaenium endlicherianum have been updated. ==References==