Brachionus calyciflorus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Rotifera
Class:	Monogononta
Order:	Ploima
Family:	Brachionidae
Genus:	Brachionus
Species:	B. calyciflorus
Binomial name
Brachionus calyciflorus Pallas, 1766

Brachionus calyciflorus is a planktonic rotifer species occurring in freshwater. It is commonly used as a model organism in toxicology, ecology and evolutionary biology.
Its advantages include the small size and short generation time (average generation time of B. calyciflorus is around 2.2 days at 24 °C).

The taxonomy of Brachionus calyciflorus is well-established based on morphological and molecular characteristics. As a member of the phylum Rotifera, it shares many features with other rotifers, including a ciliated corona and a characteristic rotary motion. Within the genus Brachionus, there are several species, including B. plicatilis, which is also commonly used in research and aquaculture. Brachionus calyciflorus is distinct from other species in the genus due to its unique calyx-shaped lorica.

Brachionus calyciflorus has a characteristic morphology that distinguishes it from other rotifer species. The body of Brachionus calyciflorus is elongated and cylindrical in shape, measuring about 160 to 350 μm in length and 80 to 160 μm in width. The head region of the body is retractable and contains a characteristic ring of cilia, called the corona, which is used for feeding and locomotion. The corona is composed of two types of cilia, the large frontal cilia and smaller ventral cilia.

One of the most distinctive features of Brachionus calyciflorus is its lorica, or outer shell. The lorica of Brachionus calyciflorus is formed from two separate plates, with the upper plate forming a calyx-like structure over the head region of the body. The lower plate is elliptical in shape and covers the rest of the body. The lorica provides structural support and protection to the rotifer.

Brachionus calyciflorus has a well-developed digestive system, with an elongated pharynx and a muscular stomach. The reproductive system of the rotifer is also well-developed, with a pair of ovaries and testes located in the posterior part of the body.

Overall, the distinctive morphology of Brachionus calyciflorus plays an important role in its feeding, locomotion, reproduction, and adaptation to its aquatic environment.

The life cycle of Brachionus calyciflorus begins with the hatching of eggs, which are either fertilized or produced by parthenogenesis. The juveniles that hatch from these eggs, called "amictic" females, are diploid and develop into reproductive females without undergoing meiosis, meaning that they produce clones of themselves.

Once the food supply becomes scarce, some amictic females switch to a meiotic mode of reproduction, producing haploid male offspring. These males then fertilize the haploid eggs, laid by the female offspring, leading to the production of diploid resting eggs, which remain dormant in the sediment until the environmental conditions become suitable for hatching. In response to suitable environmental conditions, the resting eggs hatch into diploid amictic females, starting a new cycle.

However, when the food supply remains abundant, the amictic females continue to reproduce asexually, producing new clones of themselves through multiple generations, leading to high population densities.

During the life cycle of Brachionus calyciflorus, there are several stages and instars, including neonate, juvenile, pre-adult, and adult stages. The duration of each stage can vary depending on environmental factors such as temperature, food supply, and population density. In ideal conditions, the life cycle of Brachionus calyciflorus can be as short as 2–3 days.

Brachionus calyciflorus is a freshwater rotifer species that is widely distributed around the world. It is commonly found in a range of freshwater environments, including ponds, lakes, streams, and rivers.

This species is euryhaline, meaning it can tolerate a wide range of salinities, and can be found in both fresh and brackish water habitats. It can also tolerate various environmental conditions such as pH, water temperature, and oxygen levels.

Brachionus calyciflorus is a cosmopolitan species, meaning it is found in many regions of the world, including North and South America, Europe, Asia, Australia, and Africa. It has been reported in a range of countries, including the United States, Canada, Brazil, Spain, France, Sweden, Russia, and Japan.

In addition to its natural distribution, Brachionus calyciflorus is commonly used in aquaculture, where it is reared in laboratory cultures to feed fish and other aquatic organisms. It is also used in ecotoxicology studies as a test organism due to its short life cycle and sensitivity to environmental pollutants.

Brachionus calyciforus is an important zooplankton species that plays a significant role in freshwater ecosystems. Here are some of the reasons why:

1. Food source: Brachionus calyciflorus is an important food source for many aquatic organisms such as fish, amphibians, and invertebrates. It is also used as a live food for aquarium fish.
2. Studying environmental changes: Brachionus calyciflorus can serve as an indicator of environmental changes in water bodies. Monitoring population dynamics of Brachionus calyciflorus can help assess the health of aquatic systems and detect any changes that may occur as a result of pollution or climate change.
3. Toxicity testing: Brachionus calyciflorus is widely used in ecotoxicological studies due to its sensitivity to toxic substances. It is used to test the effects of different substances on aquatic organisms, and to assess the potential risk to human health and the environment.
4. Bioremediation: Brachionus calyciflorus is known to feed on harmful algae and bacteria that can cause water quality issues. As a result, it is considered a potential agent for bioremediation of polluted water bodies.

In summary, Brachionus calyciflorus has ecological, scientific, and potential biotechnological importance.

Culturing Brachionus calyciflorus involves growing this species of rotifer in a controlled environment. Here are some important factors to consider when culturing Brachionus calyciflorus:

1. Culture vessel: Brachionus calyciflorus can be cultured in a variety of vessels such as laboratory-grade glassware, plastic containers, and aquariums. The culture vessel should be clean and have a large surface area to promote growth.
2. Temperature: The optimal temperature for culturing Brachionus calyciflorus is between 20 °C to 28 °C. Higher temperatures can lead to a decrease in growth rate and reproduction, while lower temperatures can lead to a decrease in overall biomass.
3. Light: Brachionus calyciflorus requires a light source with a 12-hour light and dark cycle. Illumination can be artificial or natural, with a light intensity of 2,000 to 4,000 lux.
4. Feeding: Brachionus calyciflorus feeds on microalgae and bacteria, and thus, it is important to provide a food source. Some commonly used microalgae for Brachionus calyciflorus cultivation include Chlorella vulgaris, Scenedesmus sp., and Nannochloropsis sp.
5. Water quality: The pH of culture water for Brachionus calyciflorus should be maintained between 6.5 and 7.5, and the salinity level should be between 0.5 and 5 parts per thousand.
6. Harvesting: Brachionus calyciflorus can be harvested using a fine-mesh filter or by centrifugation. The harvested rotifers can then be used as a live food source for other aquatic organisms or as a sample for experiments.

In summary, culturing Brachionus calyciflorus requires careful maintenance of optimal temperature, lighting, feeding, water quality, and harvesting to ensure consistent growth and high biomass production.

Brachionus calyciflorus normally reproduces by cyclical parthenogenesis.^[1]
Transitions to obligate parthenogenesis have been described. Obligate parthenogens were homozygous for a recessive allele, which caused inability to respond to the chemical signals that normally induce sexual reproduction in this species.^[2]

Like the Brachionus plicatilis cryptic species complex Brachionus calyciflorus seems also to be a species complex consisting of more than one species.^[3][4]

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• Wang, W., Xu, W., and Yang, L. (2015). Optimization of culture conditions for Brachionus calyciflorus (Rotifera) and assessment of its potentials as food for larval ornamental fish. Aquaculture Research 46, 843–855.
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