Cryptomonad
Encyclopedia
The cryptomonads are a group of algae
, most of which have plastids
. 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 may exhibit mixotrophy.
s called ejectisomes or ejectosomes, 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 ejectisomes, visible under the light microscope, are associated with the pocket; smaller ones occur underneath the periplast, the cryptophyte-specific cell surrounding.
Cryptomonads have one or two plastids, except for Chilomonas, which has leucoplast
s and Goniomonas (formerly Cyathomonas) which lacks plastids entirely. These contain chlorophyll
s a and c, together with phycobiliprotein
s 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.
A few cryptomonads, 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 resting stages with rigid cell walls (cysts) to survive unfavorable conditions. Cryptomonad 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 crista
e, and mitosis
is open; sexual reproduction
has also been reported.
s because of their (seemingly) similar pigmentation. Later botanists treated them as a separate division, Cryptophyta, while zoologists treated them as the flagellate order Cryptomonadida. There is considerable evidence that cryptomonad chloroplasts are closely related to those of the heterokont
s and haptophyte
s, 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 kingdom Chromalveolata and to form together with the Haptophyta the group Hacrobia
.
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.
s, have been considered as part of the Cryptophyta since katablepharids were described in 1939.
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, most of which have plastids
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10-50 μm
1 E-5 m
To help compare different orders of magnitude, this page lists lengths between 10−5 m and 10−4 m .Distances shorter than 10 µm* 10 µm — width of cotton fibre...
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
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
.
Some may exhibit mixotrophy.
Characteristics
Cryptomonads are distinguished by the presence of characteristic extrusomeExtrusome
Extrusomes are membrane-bound structures in some eukaryotes which, under certain conditions, discharge their contents outside the cell. There are a variety of different types, probably not homologous, and serving various functions....
s called ejectisomes or ejectosomes, 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 ejectisomes, visible under the light microscope, are associated with the pocket; smaller ones occur underneath the periplast, the cryptophyte-specific cell surrounding.
Cryptomonads have one or two plastids, except for Chilomonas, which has leucoplast
Leucoplast
Leucoplasts are a category of plastid and as such are organelles found in plant cells. They are non-pigmented, in contrast to other plastids such as the chloroplast....
s and Goniomonas (formerly Cyathomonas) which lacks plastids entirely. These contain chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
s a and c, together with phycobiliprotein
Phycobiliprotein
Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae that capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores...
s 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
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
called a nucleomorph
Nucleomorph
Nucleomorphs are small, reduced eukaryotic nuclei found in certain plastids. So far, only two groups of organisms are known to contain a nucleomorph: the cryptomonads of the supergroup Chromista and the chlorarachniophytes of the supergroup Rhizaria. The nucleomorphs support the endosymbiotic...
between the middle two. This indicates that the plastid was derived from a eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
symbiont, shown by genetic studies to have been a red alga.
A few cryptomonads, such as Cryptomonas
Cryptomonas
Cryptomonas is the name-giving genus of the cryptomonads. It is common in freshwater habitats and often forms blooms in greater depths of lakes, or during winter beneath the ice. The cells are usually brownish in color, and have a slit-like furrow at the anterior...
, can form palmelloid stages, but readily escape the surrounding mucus to become free-living flagellates again. Some Cryptomonas
Cryptomonas
Cryptomonas is the name-giving genus of the cryptomonads. It is common in freshwater habitats and often forms blooms in greater depths of lakes, or during winter beneath the ice. The cells are usually brownish in color, and have a slit-like furrow at the anterior...
species may also form immotile resting stages with rigid cell walls (cysts) to survive unfavorable conditions. Cryptomonad flagella are inserted parallel to one another, and are covered by bipartite hairs called mastigonemes
Mastigonemes
Mastigonemes are lateral "hairs" found covering the flagella of heterokont and cryptophyte algae. They are approximately 15 nm in diameter, and usually consist of a tubular shaft that itself terminates in smaller "hairs". It is believed that they assist in locomotion by increasing the surface...
, formed within the endoplasmic reticulum
Endoplasmic reticulum
The endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...
and transported to the cell surface. Small scales may also be present on the flagella and cell body. The mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
have flat crista
Crista
Cristae are the internal compartments formed by the inner membrane of a mitochondrion. They are studded with proteins, including ATP synthase and a variety of cytochromes. The maximum surface for chemical reactions to occur is within the mitochondria...
e, and mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
is open; sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
has also been reported.
Classification
Originally the cryptomonads were considered close relatives of the dinoflagellateDinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...
s because of their (seemingly) similar pigmentation. Later botanists treated them as a separate division, Cryptophyta, while zoologists treated them as the flagellate order Cryptomonadida. There is considerable evidence that cryptomonad chloroplasts are closely related to those of the heterokont
Heterokont
The heterokonts or stramenopiles are a major line of eukaryotes currently containing more than 100,000 known species. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which are a primary component of plankton...
s and haptophyte
Haptophyte
The haptophytes, classified either as the Prymnesiophyta or Haptophyta, are a division of algae.The term "Haptophyceae" is sometimes used. This ending implies classification at a lower level...
s, and the three groups are sometimes united as the Chromista
Chromista
The Chromista are a eukaryotic supergroup, probably polyphyletic, which may be treated as a separate kingdom or included among the Protista. They include all algae whose chloroplasts contain chlorophylls a and c, as well as various colorless forms that are closely related to them...
. 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 kingdom Chromalveolata and to form together with the Haptophyta the group Hacrobia
Hacrobia
thumb|upright|The [[coccolithophore]] [[Gephyrocapsa]] oceanicaThe Cryptomonads-haptophytes assemblage is a monophyletic grouping of chromalveolata that are not included in the SAR supergroup.The term "Hacrobia" has been proposed for this group...
.
One suggested grouping is as follows: (1) Cryptomonas
Cryptomonas
Cryptomonas is the name-giving genus of the cryptomonads. It is common in freshwater habitats and often forms blooms in greater depths of lakes, or during winter beneath the ice. The cells are usually brownish in color, and have a slit-like furrow at the anterior...
, (2) Chroomonas
Chroomonas
Chroomonas is a cryptophyte genus. It includes the species Chroomonas placoidea, Chroomonas baltica, Chroomonas guttula and Chroomonas vectensis....
/Komma
Komma
Komma caudata is a cryptomonad, and the only described species in the genus Komma, although four or five more species may exist. Its cells are 4.5–5.5 μm wide by 7–10 μm long and bear two unequal flagella....
and Hemiselmis
Hemiselmis
Hemiselmis is a cryptophyte genus, including the species Hemiselmis andersenii....
, (3) Rhodomonas
Rhodomonas
Rhodomonas is a genus of algae.It includes the species Rhodomonas salina....
/Rhinomonas
Rhinomonas
Rhinomonas is a cryptophyte genus.It includes the species Rhinomonas pauca....
/Storeatula
Storeatula
Storeatula is a cryptophyte genus.It includes the species Storeatula major....
, (4) Guillardia/Hanusia, (5) Geminigera/Plagioselmis
Plagioselmis
Plagioselmis is a genus of cryptophytes, including the species Plagioselmis prolonga and Plagioselmis punctata....
/Teleaulax, (6) Proteomonas sulcata, (7) Falcomonas daucoides.
Katablepharids
The katablepharids, a group of heterotrophic flagellateFlagellate
Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...
s, have been considered as part of the Cryptophyta since katablepharids were described in 1939.