• Source: Cryptophyceae

The cryptophyceae are a class of algae, most of which have plastids. About 230 species are known, and they are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella.
Some exhibit mixotrophy.




Characteristics



Cryptophytes are distinguished by the presence of characteristic extrusomes called ejectosomes or ejectisomes, which consist of two connected spiral ribbons held under tension. If the cells are irritated either by mechanical, chemical or light stress, they discharge, propelling the cell in a zig-zag course away from the disturbance. Large ejectosomes, visible under the light microscope, are associated with the pocket; smaller ones occur underneath the periplast, the cryptophyte-specific cell surrounding.
Except for Chilomonas, which has leucoplasts, cryptophytes have one or two chloroplasts. These contain chlorophylls a and c, together with phycobiliproteins and other pigments, and vary in color (brown, red to blueish-green). Each is surrounded by four membranes, and there is a reduced cell nucleus called a nucleomorph between the middle two. This indicates that the plastid was derived from a eukaryotic symbiont, shown by genetic studies to have been a red alga. However, the plastids are very different from red algal plastids: phycobiliproteins are present but only in the thylakoid lumen and are present only as phycoerythrin or phycocyanin. In the case of "Rhodomonas" the crystal structure has been determined to 1.63Å; and it has been shown that the alpha subunit bears no relation to any other known phycobiliprotein.
A few cryptophytes, such as Cryptomonas, can form palmelloid stages, but readily escape the surrounding mucus to become free-living flagellates again. Some Cryptomonas species may also form immotile microbial cysts–resting stages with rigid cell walls to survive unfavorable conditions. Cryptophyte flagella are inserted parallel to one another, and are covered by bipartite hairs called mastigonemes, formed within the endoplasmic reticulum and transported to the cell surface. Small scales may also be present on the flagella and cell body. The mitochondria have flat cristae, and mitosis is open; sexual reproduction has also been reported.
The group have evolved a whole range of light-absorbing pigments, called phycobilins, which are able to absorb wavelengths that are not accessible to other plants or algae, allowing them to live in a variety of different ecological niches. An ability that originates from the evolution of a unique light‐harvesting antenna complex derived from two relict parts of the red algal phycobilisome, which was completely dismantled during the endosymbiotic process.
While cryptophytes are usually seen as asexual, sexual reproductions do occur; both haploid and diploid forms have been found. The two species Teleaulax amphioxeia and Plagioselmis prolonga are now considered to be the same species, where T. amphioxeia is the diploid form and P. prolonga is the haploid form. The diploid form is most common when there are more nutrients in the water. Two haploid cells will often fuse to form a diploid cell, mixing their genes.




Classification



The first mention of cryptophytes appears to have been made by Christian Gottfried Ehrenberg in 1831, while studying Infusoria. Later, botanists treated them as a separate algae group, class Cryptophyceae or division Cryptophyta, while zoologists treated them as the flagellate protozoa order Cryptomonadina. In some classifications, the cryptomonads were considered close relatives of the dinoflagellates because of their (seemingly) similar pigmentation, being grouped as the Pyrrhophyta. There is considerable evidence that cryptophyte chloroplasts are closely related to those of the heterokonts and haptophytes, and the three groups are sometimes united as the Chromista. However, the case that the organisms themselves are closely related is not very strong, and they may have acquired plastids independently. Currently they are discussed to be members of the clade Diaphoretickes and to form together with the Haptophyta the group Hacrobia. Parfrey et al. and Burki et al. placed Cryptophyceae as a sister clade to the green algae.
One suggested grouping is as follows: (1) Cryptomonas, (2) Chroomonas/Komma and Hemiselmis, (3) Rhodomonas/Rhinomonas/Storeatula, (4) Guillardia/Hanusia, (5) Geminigera/Plagioselmis/Teleaulax, (6) Proteomonas sulcata, (7) Falcomonas daucoides.

Class Cryptophyceae Fritsch 1937 [Cryptomonadea Stein 1878 emend. Schoenichen 1925]
Genus Wysotzkia Lemmermann 1899
Genus Urgorri Laza-Martinez 2012
Order Tetragonidiales Kristiansen 1992
Family Tetragonidiaceae Bourelly ex Silva1980
Genus Bjornbergiella Bicudo 1966
Genus Tetragonidium Pascher 1914
Order Pyrenomonadales Novarino & Lucas 1993
Family Baffinellaceae Daugbjerg & Norlin 2018
Genus Baffinella Norlin & Daugbjerg 2018
Family Chroomonadaceae Clay, Cugrens & Lee 1999
Genus ?Smithimastix Skvortzov 1969 [Smithiella Skvortzov 1968 nom. illeg.]
Genus Chroomonas Hansgirg 1885
Genus Falcomonas Hill 1991
Genus Hemiselmis Parke 1949
Genus Komma Hill 1991
Genus Nodeana Skvortzov 1968
Genus Planonephros Christensen 1978
Genus Protochrysis Pascher 1911
Family Geminigeraceae Clay, Cugrens & Lee 1999
Genus Geminigera Hill 1991
Genus Guillardia Hill & Wetherbee 1990
Genus Phia Özdikmen 2009 [Hanusia Deane et al. 1998 non Cripps 1989]
Genus Plagioselmis Butcher 1967 ex Novarino, Lucas & Morrall 1994
Genus Teleaulax Hill 1991
Family Pyrenomonadaceae Novarino & Lucas 1993
Genus Proteomonas Hill & Wetherbee 1986
Genus Rhinomonas Hill & Wetherbee 1988
Genus Rhodomonas Karsten 1898 [Pyrenomonas Santore 1984]
Genus Storeatula Hill 1991
Order Cryptomonadales Pascher 1913
Family ?Butschliellaceae Skvortzov 1968
Genus Butschliella Skvortzov 1968
Genus Skvortzoviella Bourelly 1970
Family ?Cyathomonadaceae Pringsheim 1944
Genus Cyathomonas de Fromentel 1874
Family ?Hilleaceae Pascher 1967
Genus Calkinsiella Skvortzov 1969
Genus Hillea Schiller 1925
Family ?Pleuromastigaceae Bourrelly ex Silva 1980
Genus ?Opisthostigma Scherfffel 1911
Genus Pleuromastix Scherffel 1912 non Namyslowski 1913
Genus Xanthodiscus Schewiakoff 1892
Family Cryptomonadaceae Ehrenberg 1831 [Campylomonadaceae Clay, Kugrens & Lee 1999; Cryptochrysidaceae Pascher 1931]
Genus ?Chilomonas Ehrenberg 1831
Genus ?Protocryptochrysis Skvortzov 1969
Genus Cryptella Pascher 1929
Genus Cryptochloris Schiller 1925
Genus Cryptochrysis Pascher 1911
Genus Cryptomonas Ehrenberg 1832 [Campylomonas Hill 1991]
Genus Cyanomastix Lackey 1936
Genus Isoselmis Butcher 1967
Genus Kisselevia Skvortzov 1969
Genus Meyeriella Skvortzov 1968
Genus Olivamonas Skvortzov 1969
Genus Protocryptomonas Skvortzov 1969 ex Bicudo 1989




References






External links


Tree of Life: Cryptomonads

Kata Kunci Pencarian:

• Chromista
• Hacrobia
• Haptista
• Cryptophyceae
• Cryptomonad
• Rollomonadia
• Cryptomonas
• Flagellate
• Cryptista
• Mastigoneme
• Cryptochrysis
• Flagellum
• List of eukaryotic picoplankton species