Dasycladales is an order 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 Cummin ...

. It contains two families, the

Dasycladaceae The Dasycladaceae is one of the two extant families of green algae of the order Dasycladales. When found in Palaeozoic limestones, they typically indicate depositional depth of less than 5m.See the NCBI The National Center for Biotechnology ...

and the

Polyphysaceae The Polyphysaceae is a taxonomic family of green algae, one of three families in the order Dasycladales Dasycladales is an order of large unicellular green algae in the class Ulvophyceae. It contains two families, the Dasycladaceae and the ...

. 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 Nucle ...

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 resu ...

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 A gametangium (plural: gametangia) is an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants. In contrast to gametogenesis in animals, a gametangium is a haploi ...

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. The ...

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 Cyclocrinitids are an early (mid-Ordovician–early-Silurian) Dasycladalean algae, resembling but probably not closely related to the Receptaculitids. References Dasycladales {{silurian-plant-stub ...

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 ''Carnets Geol.'' (previously ''Carnets de Géologie'' or ''Carnets de Géologie - Notebooks on Geology'') is an electronic journal that publishes in the field of geosciences, and particularly paleontology, stratigraphy, and sedimentology. The ope ...

'', 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.- , ''

'', Brest, Special Publication 2009/01
CG2009_SP01
, 180 p., 2 figs., 29 pls. Chlorophyta orders {{Ulvophyceae-stub