Dasycladales is an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

of large unicellular green algae in the class

Ulvophyceae The Ulvophyceae or ulvophytes are a class of green algae, distinguished mainly on the basis of Ultrastructure, ultrastructural morphology, Biological life cycle, life cycle and molecular phylogenetics, molecular phylogenetic data. The sea lettu ...

. It contains two families, the Dasycladaceae and the

Polyphysaceae The Polyphysaceae is a taxonomic family (biology), family of green algae, one of three families in the order Dasycladales. For single-celled organisms, they are huge, growing to nearly a foot long in some cases. References

Dasycladales ...

. These single celled algae are from 2 mm to 200 mm long. They live on substrates in shallow warm (>20 °C) euhaline tropical marine waters, usually less than 20 meters deep, and protected from waves. They are very large cells. They are able to attain these sizes without numerous internal cell wells because they build calcium carbonate shells around themselves. They contain only one nucleus in their vegetative stage, which remains in the bottom of the cell in the holdfast at the substrate. Only when they are ready to produce

gametes A gamete ( ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the Ge ...

does the nucleus undergo

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

and then numerous

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

into many nuclei which then migrate into the

gametangia A gametangium (: gametangia) is a sex organ or cell in which gametes are produced that is found in many multicellular protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists ...

at the top of the alga. Because the nucleus is safely hidden in the holdfast, the cells easily regenerate if the top portions are broken off. These algae are notable for having an intracellular network of 10 nm proteinaceous filaments, possibly for the storage and transport of ribonucleoprotein particles. Because of all these properties, and the fact that they are easy to manipulate they have been favorite organisms in the study of the role of the nucleus vs the unnucleated

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

in the behavior of cells. Receptaculitid

Mineralization

Dasyclads mineralize in aragonite or high-magnesium calcite (never both in the same species); some extant examples also contain extracellular secretions of weddellite (calcium oxalate, ), secreted in the mucilage layer. Calcification can occur in (i) cell walls, potentially continuing into cell lumina; (ii), vacuoles, before transport to cell walls or mucilage; (iii) within cell lumens; (iv) the mucilage layer, (v) externally to the mucilage layer; typically without biological mediation. The calcium carbonate typically forms needle-like crystals, sometimes forming layers with different orientations corresponding to later stages of mineralization, but idiosyncratic microstructures characterize specific taxa.

Fossil record

Cyclocrinitids are among their earliest fossil representatives. Proposed Cambrian representatives (questionable) include: - ''Cambroporella'' - ''Amgaella'' - ''Yakutina'' - ''Seletonella'' - ''Mejerella''

References

External links

* Berger, Sigrid (2006).- Photo-Atlas of living Dasycladales.- , '' Carnets de Géologie'', Brest, Book / Livre 2006/02
CG2006_BOOK_02
, 348 p., 1 fig., 332 micrographs. * Génot, Patrick (2009).- Cenozoic Dasycladales. A photo-atlas of Lutetian species from French Cenozoic basins.- , '' Carnets de Géologie'', Brest, Special Publication 2009/01
CG2009_SP01
, 180 p., 2 figs., 29 pls. Chlorophyta orders {{Ulvophyceae-stub