The cryptophyceae are a class of

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

, 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 A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. 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

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

s ''a'' and ''c'', together with

phycobiliprotein Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae (rhodophytes, cryptomonads, glaucocystophytes). They capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are ...

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 The cell nucleus (; : nuclei) is a membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have #Anucleated_cells, ...

called a nucleomorph between the middle two. This indicates that the plastid was derived from a

eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

symbiont, shown by genetic studies to have been a

red alga Red algae, or Rhodophyta (, ; ), make up one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest Phylum, phyla of algae, containing over 7,000 recognized species within over 900 Genus, genera amidst ongoing taxon ...

. 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 Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist ...

. 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 cyst A microbial cyst is a resting or dormant stage of a microorganism, that can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed and the cell ceases all activities like feeding and locomotion. ...

s–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 The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...

and transported to the cell surface. Small scales may also be present on the flagella and cell body. The

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

have flat

crista A crista (; : cristae) is a fold in the inner mitochondrial membrane, inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large a ...

e, and

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

is open;

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

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

CSIRO ScienceImage 7234 microalgal cultures

The first mention of cryptophytes appears to have been made by

Christian Gottfried Ehrenberg Christian Gottfried Ehrenberg (19 April 1795 – 27 June 1876) was a German Natural history, naturalist, zoologist, Botany, botanist, comparative anatomist, geologist, and microscopy, microscopist. He is considered to be one of the most famous an ...

in 1831, while studying Infusoria. Later, botanists treated them as a separate

group, class Cryptophyceae or division Cryptophyta, while zoologists treated them as the

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...

protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...

order Cryptomonadina. In some classifications, the cryptomonads were considered close relatives of the

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

s 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

heterokont The stramenopiles, also called heterokonts, are protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, an ...

s and haptophytes, and the three groups are sometimes united as the

Chromista Chromista is a proposed but polyphyletic obsolete Biology, biological Kingdom (biology), kingdom, refined from the Chromalveolata, consisting of single-celled and multicellular eukaryotic species that share similar features in their Photosynthesi ...

. 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 Diaphoretickes is a major group of eukaryote, eukaryotic organisms spanning over 400,000 species. The majority of the earth's biomass that carries out photosynthesis belongs to Diaphoretickes. In older classification systems, members of the Diaph ...

and to form together with the

Haptophyta The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae. The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...

the group

Hacrobia The cryptomonads-haptophytes assemblage is a proposed but disputed monophyletic grouping of unicellular eukaryotes that are not included in the SAR supergroup. Several alternative names have been used for the group, including Hacrobia (derived ...

. Parfrey et al. and Burki et al. placed Cryptophyceae as a sister clade to the

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

. One suggested grouping is as follows: (1) '' Cryptomonas'', (2) '' Chroomonas/ Komma'' and '' Hemiselmis'', (3) ''

Rhodomonas ''Rhodomonas'' is a genus of cryptomonads. It is characterized by its red colour, the square-shaped plates of its inner periplast, its short furrow ending in a gullet, and a distinctly shaped chloroplast A chloroplast () is a type of memb ...

/ Rhinomonas/ Storeatula'', (4) '' Guillardia/ Hanusia'', (5) '' Geminigera/ Plagioselmis/ Teleaulax'', (6) '' Proteomonas sulcata'', (7) '' Falcomonas daucoides''. * Class Cryptophyceae Fritsch 1937 ryptomonadea Stein 1878 emend. Schoenichen 1925** Genus '' Wysotzkia'' Lemmermann 1899 ** Genus '' Urgorri'' Laza-Martinez 2012 ** Order

Tetragonidiales Tetragonidiaceae is a family of cryptomonads which includes two genera. Members of Tetragonidiaceae are distinguished from other cryptomonads by reproduction occurring in a non-motile vegetative phase, as well as the formation of multicellular f ...

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.">Smithiella.html" ;"title="'Smithiella">'Smithiella'' Skvortzov 1968 nom. illeg.**** Genus '' Chroomonas'' Hansgirg 1885 **** Genus ''Falcomonas'' Hill 1991 **** Genus '' Hemiselmis'' Parke 1949 **** Genus ''Komma (alga), 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">' 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 Geminigeraceae is a family of cryptophytes containing the five genera '' Geminigera'', '' Guillardia'', ''Hanusia'', ''Proteomonas'' and ''Teleaulax''. They are characterised by chloroplasts containing Cr-phycoerythrin 545, and an inner peri ...

'' Hill & Wetherbee 1986 **** Genus '' Rhinomonas'' Hill & Wetherbee 1988 **** Genus ''

'' Karsten 1898 'Pyrenomonas'' Santore 1984">Pyrenomonas.html" ;"title="'Pyrenomonas">'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 ampylomonadaceae Clay, Kugrens & Lee 1999; Cryptochrysidaceae Pascher 1931] **** Genus ?'' Chilomonas'' Ehrenberg 1831 **** Genus ?''Protocryptochrysis'' Skvortzov 1969 **** Genus '' Cryptella'' Pascher 1929 **** Genus ''

Cryptochloris ''Cryptochloris'' is a genus of golden moles, containing the two species De Winton's golden mole (''Cryptochloris wintoni'') and Van Zyl's golden mole (''Cryptochloris zyli''). References

Afrosoricida Mammal genera Taxonomy articles cr ...

'' Schiller 1925 **** Genus '' Cryptochrysis'' Pascher 1911 **** Genus '' Cryptomonas'' Ehrenberg 1832 'Campylomonas'' Hill 1991">Campylomonas.html" ;"title="'Campylomonas">'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
{{Taxonbar, from=Q21281984, from2=Q18668642, from3=Q488032 Taxa named by Thomas Cavalier-Smith