Dasycladales is an

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

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 ultrastructural morphology, life cycle and molecular phylogenetic data.Graham LE, Graham JM, Wilcox LW (2009) ''Algae''. 2nd Edition. Benjamin Cumming ...

. It contains two families, the Dasycladaceae and the Polyphysaceae. 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 Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

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 (; , ultimately ) 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. In species that produce ...

does the nucleus undergo

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...

and then numerous

mitoses In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintai ...

into many nuclei which then migrate into the gametangia 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 In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

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, CaC2O4), 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