Dasycladales
Large unicellular green algae that build calcium carbonate shells.
Dasycladales are an order of large, single-celled green algae belonging to the class Ulvophyceae. Two families are still alive today: Dasycladaceae and Polyphysaceae. These organisms range from 2 mm to 200 mm in length. They live attached to substrates in warm, shallow, salty tropical marine waters—typically above 20 °C, less than 20 meters deep, and sheltered from wave action. Despite being just one cell, they reach such sizes without many internal walls because they build a shell of calcium carbonate around themselves.
During their vegetative stage, each cell has only one nucleus, which stays at the bottom inside the holdfast attached to the substrate. Only when the alga is ready to produce gametes does that nucleus undergo meiosis, followed by many mitoses, creating many nuclei that then move into the gametangia at the top of the cell. Because the nucleus is safely tucked away in the holdfast, the cell can easily regrow if the upper parts break off.
These algae also have an internal network of protein filaments, each about 10 nanometers thick, which may store and transport ribonucleoprotein particles. Thanks to all these traits—plus the fact they are easy to handle—Dasycladales have been favorite subjects for studying how the nucleus and the rest of the cytoplasm each contribute to cell behavior.
**Mineralization** Dasyclads mineralize using either aragonite or high-magnesium calcite (never both in the same species). Some living species also secrete weddellite (calcium oxalate) into the mucilage layer around the cell. Calcification can happen in several places: inside cell walls (sometimes continuing into the cell lumen), inside vacuoles (before being moved to walls or mucilage), within the cell lumen itself, in the mucilage layer, or outside the mucilage layer—typically without direct biological control. The calcium carbonate usually forms needle-like crystals, sometimes arranged in layers with different orientations that reflect later stages of mineralization. Specific taxa have their own distinctive microstructures.
**Fossil record** Because they deposit calcium carbonate around themselves, dasycladalean algae are well preserved as fossils. The earliest known fossil representatives are the cyclocrinitids. Some proposed Cambrian examples (though uncertain) include *Cambroporella*, *Amgaella*, *Yakutina*, *Seletonella*, and *Mejerella*.
Quick Facts
- Taxon
- Dasycladales
Facts from the source article.
Lore & Background
Dasycladales are very large single cells that live on substrates in shallow, warm, protected tropical marine waters. They contain only one nucleus in their vegetative stage, which remains in the holdfast at the bottom of the cell. When ready to produce gametes, the nucleus undergoes meiosis and then numerous mitoses, and the resulting many nuclei 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 also notable for having an intracellular network of 10 nm proteinaceous filaments, possibly for the storage and transport of ribonucleoprotein particles.
Reader's Guide
Dasycladales are significant as model organisms in the study of the role of the nucleus versus the unnucleated cytoplasm in cell behavior, due to their large size, ease of manipulation, and the safe location of the nucleus in the holdfast. Their ability to mineralize calcium carbonate—in aragonite or high-magnesium calcite, never both in the same species—makes them well-represented in the fossil record. Calcification can occur in cell walls, vacuoles, cell lumens, the mucilage layer, or externally to the mucilage layer, typically without biological mediation. The calcium carbonate forms needle-like crystals, sometimes in layers with different orientations, and idiosyncratic microstructures characterize specific taxa. Their fossil record includes early representatives such as Cyclocrinitids, with several proposed but questionable Cambrian forms including Cambroporella, Amgaella, Yakutina, Seletonella, and Mejerella.
Did You Know?
- Dasycladales are single-celled algae that can reach up to 200 mm in length.
- They build calcium carbonate shells to attain large sizes without numerous internal cell walls.
- The single nucleus remains in the holdfast during the vegetative stage, allowing regeneration if the top is broken off.
- Some extant dasyclads secrete weddellite (calcium oxalate) in the mucilage layer.
Frequently Asked Questions
What are Dasycladales?
Dasycladales is an order of green macroalgae in the class Ulvophyceae, composed of large single-celled organisms. Rather than being made of many small cells, each individual is one giant cell wrapped in a calcium carbonate shell that gives it structural support.
How big can Dasycladales get?
These single cells span a size range from 2 mm up to 200 mm in length. They reach that scale without internal walls or compartmentalization, relying entirely on their external mineral shell for rigidity.
Where do Dasycladales live?
They attach to hard substrates in warm tropical marine settings where temperatures exceed 20 °C and salinity is moderate (euhaline). They favor sheltered, shallow waters generally under 20 meters deep, staying out of heavy wave action.
What are the living families of Dasycladales?
Two families still exist today: Dasycladaceae and Polyphysaceae. Each species builds its shell from either aragonite or high-magnesium calcite—never a mix of both—though some also deposit a mineral called weddellite.
What is the oldest fossil evidence linked to Dasycladales?
The earliest fossil representatives associated with this order are the Cyclocrinitids. In their vegetative stage, every Dasycladales cell carries just a single nucleus, a feature that has persisted throughout the group's long evolutionary history.
More in Marine Green Macroalgae, Part 2 1-24
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