ARTEMIA (GENUS): CHARACTERISTICS, HABITAT, REPRODUCTION - BIOLOGY - 2024

Artemia is a genus of crustaceans that belongs to the Artemiidae family. They are very small in size and are present in zooplankton in a wide number of habitats throughout the world.

It was first described by the English zoologist William Leach. It is made up of a total of eleven species, among these the best known are Artemia salina and Artemia franciscana.

Artemia population. Source: Atro S / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Animals of this genus are of great importance in ecosystems, since as part of zooplankton they constitute food for fish and other aquatic animals. Taking this into account, they are used in aquaculture, growing them to feed fish that are used for commercial purposes.

characteristics

Individuals of the genus Artemia are multicellular eukaryotic organisms. The cells that make up your different organs and tissues specialize in specific functions. They also have a cell nucleus within which the genetic material (DNA) is well protected.

Likewise, they are considered triblastic and coelomed. In this sense, triblastic organisms are those that, during their embryonic development, present the three germ layers: endoderm, ectoderm and mesoderm. They also have an internal cavity called a coelom. They have bilateral symmetry because they are made up of two equal halves.

Regarding their reproduction and life cycle, it can be said that they reproduce, both sexually and asexually. Fertilization is internal and they can be oviparous or ovoviviparous. Their development is indirect, since they present different stages, between the egg and the adult animal.

They are heterotrophic organisms because they cannot synthesize their nutrients, so they feed on small microscopic algae that are present in water currents.

Morphology

The Artemia genus is made up of animals that measure approximately 13 mm. Its body is translucent and quite narrow.

The body is made up of three areas or zones: head, thorax and abdomen. On the head are the antennae, which in the case of males are modified in the form of pincers. This allows them to support the female during the fertilization process.

On the head there is also a pair of eyes that are compound.

The thorax is divided into several segments, from each a pair of appendages emerge. These are known as thoracopods and are of great help in the locomotion of the animal and in the creation of streams of water to feed.

Male and female Artemia specimens. Source: © Hans Hillewaert

The last segment of the animal's body is the abdomen, which is also divided into several segments. The first segments are the genitals. In the case of the female, a kind of bag is observed that is known as an ovigerous sac. There you can see the contained eggs.

Taxonomy

The taxonomic classification of Artemia is as follows:

• Domain: Eukarya
• Animalia Kingdom
• Phylum: Arthropoda
• Subphylum: Crustacea
• Class: Brachiopoda
• Order: Anostraca
• Family: Artemiidae
• Genus: Artemia

Habitat and distribution

Artemia salina

There are other species, such as Artemia monica from Mono Lake (California), that are only confined to a single location.

Despite this, the environments in which these crustaceans are found share certain characteristics in common. The first of them is that they are saline rivers or closed bodies of water that do not have direct communication to the sea, such as the so-called endorheic lakes.

Another of these characteristics is that they have a high level of salinity. In order to survive in these environments, these crustaceans have an internal regulation system.

Reproduction

In organisms of the genus Artemia it is possible to find the two types of reproduction that exist: asexual and sexual.

- Asexual reproduction

This type of reproduction does not require the union of male and female sex cells (gametes). Consequently, you do not need the interaction of two specimens.

In asexual reproduction, an individual or individuals are generated from a parent that are genetically and physically exactly the same as the parent.

Now, there are many mechanisms through which asexual reproduction can occur. In the case of crustaceans of this genus, the asexual reproduction process observed is parthenogenesis.

Parthenogenesis

It is a fairly common asexual reproduction mechanism in arthropods. It consists of the development of individuals from the unfertilized ovules of virgin females. In this case, female individuals will always be obtained.

However, in species of the genus Artemia, a particular type of parthenogenesis is observed, called automixis. In this process, two ovules (haploid) that originated in the same meiosis fuse to give rise to a diploid zygote, from which an adult individual develops.

- Sexual reproduction

In this type of reproduction, the interaction of two individuals of the opposite sex occurs and the fusion of two sex cells, a female (ovum) and a male (sperm). The process through which both cells unite is called fertilization.

Fertilization

The type of fertilization that is observed in these crustaceans is internal, that is, it occurs inside the body of the female. Its development is indirect, because in order to reach the adult stage it is necessary to go through a larval stage, in which it undergoes some molts.

Eggs

The environmental conditions of the habitat in which it is found have a great influence on the reproductive process. When these conditions, especially salinity levels, are optimal, these animals behave as ovoviviparous, that is, the eggs develop inside the female.

On the contrary, when the salinity levels decrease, they act as oviparous. This means that the female releases the eggs to the external environment. These eggs are covered by a kind of protective capsule, which turns them into cysts.

Encysted egg of Artemia salina. Source: Adrian J. Hunter / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Cysts can remain unchanged for a long time, and they are resistant to harsh environmental conditions.

Larvae

Once the eggs hatch, the lavas come out. It is important to mention that there are several stages of larvae, the nauplii and the metanauplius.

Nauplii are characterized by the fact that the body has not yet segmented. In some species, such as Artemia salina, they have an orange coloration. Likewise, it is possible that during this phase the individual experiences a molt, so there will be two nauplii: 1 and 2.

Later, the nauplii undergo certain changes and the appendages (thoracópods) begin to appear, which will help the adult crustacean to move. This stage is called the metanauplius.

Pre adult and adult

The metanauplius begins to transform, acquiring the characteristics of an adult individual. Here there is an intermediate stage known as pre-adult, in which all the distinctive characteristics of an adult have not yet developed. In the pre-adult, the most striking sign is the development of the antennae.

Eventually, the pre-adult matures and acquires the permanent characteristics of an adult. The most important thing about this phase is that he is sexually mature and can reproduce.

Nutrition

Members of the genus Artemia are filter feeders. They feed on organic particles that are part of the phytoplankton.

The way they do it is as follows: with the movement of their thoracopods they generate water currents, which allow them to have access to the different food particles that may be there.

It is important to note that the different species of Artemia feed constantly. Their food is mainly constituted by microscopic algae that, as previously mentioned, integrate phytoplankton.

Genus species

Artemia salina

This is the best known species of this crustacean. This is probably due to the fact that it is found throughout the planet, with the sole exception of Antarctica. Likewise, it is considered the type species when speaking of the genus Artemia.

Specimens of Artemia salina. Source: Unknown author / Public domain

It is a highly known and studied species because it is also used quite frequently in the aquaculture industry. It is cultivated for the purpose of feeding it to fish that are raised for commercial purposes.

Franciscan Artemia

Like Artemia salina, this species is very abundant and used in aquaculture as fish food. It is used because it has a very high growth rate.

It is very abundant in the Caribbean and North America, as well as the islands of the Pacific. It is also possible to obtain copies in Australia. The preferred habitat of this species is represented by bodies of water that have a high percentage of salinity.

Artemia monica

This is an endemic species found exclusively in Mono Lake in the state of California, United States.

It can be said that this species is seasonal, since it is extremely abundant during the summer months and its population declines in winter. Then it increases again in spring and reaches its maximum peak in summer.

Artemia sinica

This is another species of the genus Artemia that is widely known in the Asian continent, specifically in Central Asia and particularly in China.

References

1. Abatzopolulos T., Beardmore, J., Clegg, J and Sorgeloos, P. (2010). Artemia. Basic and appliedd biology. Kluwer Academic Publishers.
2. Brusca, RC & Brusca, GJ, (2005). Invertebrates, 2nd edition. McGraw-Hill-Interamericana, Madrid
3. Curtis, H., Barnes, S., Schneck, A. and Massarini, A. (2008). Biology. Editorial Médica Panamericana. 7th edition.
4. Godínez, D., Gallo, M., Gelabert, R., Díaz, A., Gamboa, J., Landa, V. and Godínez, E. (2004). Larval growth of Artemia franciscana (Kellog 1906) fed with two species of live microalgae. Tropical animal husbandry. 22 (3)
5. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill.
6. Nougué, O., Rode, N., Jabbour, R., Ségard, A., Chevin, L., Haag, C. and Leormand, T. (2015). Automixis in Artemia: soling a century old controversy. Joural of Evolutionary Biology.