Euglenophyceae (ICNafp, proposed as a class) or Euglenea (ICZN, proposed as a class) is an unranked clade of single-celled algae belonging to the phylum Euglenozoa. They have chloroplasts originated from an event of secondary endosymbiosis with a green alga. They are distinguished from other algae by the presence of paramylon as a storage product and three membranes surrounding each chloroplast.
Description Euglenophyceae are unicellular algae, protists that contain chloroplasts. Their chloroplasts originated from a secondary endosymbiosis with a green alga, particularly from the order Pyramimonadales, and contain chlorophylls a and b. Some have secondarily lost this ability and evolved toward osmotrophy. In addition to photosynthetic plastids, most species have a photosensitive eyespot.
Ecology Euglenophyceae are mainly present in the water column of freshwater habitats. They are abundant in small eutrophic water bodies of temperate climates, where they are capable of forming blooms, including toxic blooms such as those caused by Euglena sanguinea. In tropical climate, blooms are common in ponds. In marine environments they have been reported in a lower amount. Some species are capable of migrating vertically through the sand along with the cycles of ocean tides. Two lineages of Euglenophyceae are part of the marine plankton: Rapazida and Eutreptiales. Eutreptiales can amount up to 46% of the total phytoplankton biomass when blooming in eutrophic coastal waters.
Classification
Euglenophyceae encompasses three taxonomic groups: the mixotrophic Rapaza viridis and two mainly phototrophic orders, Euglenales and Eutreptiales. The classification is as follows (species numbers based on AlgaeBase):
Order Euglenales Leedale, 1967 emend. Marin & Melkonian, 2003 Family Euglenaceae [Euglenidae] Dujardin, 1841 emend. Kim et al., 2010 Colacium Ehrenberg, 1834 – 17 spp. Cryptoglena Ehrenberg, 1831 – 11 spp. Euglena Ehrenberg, 1830 – 174 spp. Euglenaformis Bennett & Triemer, 2014 – 3 spp. Euglenaria Karnkowska, Linton & Kwiatowski, 2010 – 4 spp. Monomorphina Mereschkowsky, 1877 – 17 spp. Strombomonas Deflandre, 1930 – 99 spp. Trachelomonas Ehrenberg, 1834 – 410 spp. Family Phacaceae [Phacidae] Kim, Triemer & Shin, 2010 Discoplastis Triemer, 2006 – 6 spp. Flexiglena Zakryś & Łukomska, 2020 – 1 sp. Lepocinclis Perty, 1849 – 90 spp. Phacus Dujardin, 1841 – 188 spp. Order Eutreptiales Family Eutreptiaceae [Eutreptiidae] Hollande, 1942 Eutreptia Perty, 1852 – 11 spp. Eutreptiella da Cunha, 1914 – 9 spp. Order Rapazida Cavalier-Smith, 2016 Family Rapazidae Cavalier-Smith, 2016 Rapaza Yamaguchi, Yubuki & Leander, 2012 – 1 sp. Several genera assigned to Euglenophyceae are considered incertae sedis, because the lack of genetic data makes their phylogenetic position unresolved:
Ascoglena Stein, 1878 – 4 spp. Euglenamorpha Wenrich, 1924 – 2 spp. Euglenopsis Klebs, 1892 – 11 spp. Glenoclosterium Carter, 1869 – 1 sp. Hegneria Brumpt & Lavier, 1924 – 1 sp. Klebsina Silva, 1961 – 1 sp. Euglenocapsa Steinecke, 1932 – 1 sp. Menoidium Perty, 1852 – 28 spp. Parmidium Christen, 1962 – 10 spp.
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