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Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individual is genetically and physically similar to the parent or an exact clone of the parent. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many eukaryotic organisms including plants, animals, and fungi can also reproduce asexually. In vertebrates, the most common form of asexual reproduction is parthenogenesis, which is typically used as an alternative to sexual reproduction in times when reproductive opportunities are limited. Komodo dragons and some monitor lizards can also reproduce asexually.
The flatworms, flat worms, Platyhelminthes, or platyhelminths are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates, and have no specialized circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening for both ingestion and egestion ; as a result, the food cannot be processed continuously.
Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual.
Hemichordata is a phylum which consists of triploblastic, enterocoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes: Enteropneusta, and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. The class Graptolithina, formerly considered extinct, is now placed within the pterobranchs, represented by a single living genus Rhabdopleura.
Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.
A planarian is one of the many flatworms of the traditional class Turbellaria. It usually describes free-living flatworms of the order Tricladida (triclads), although this common name is also used for a wide number of free-living platyhelminthes. Planaria are common to many parts of the world, living in both saltwater and freshwater ponds and rivers. Some species are terrestrial and are found under logs, in or on the soil, and on plants in humid areas.
Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning, where an organism is split into fragments. Each of these fragments develops into mature, fully grown individuals that are clones of the original organism.
Botryllus schlosseri is a colonial ascidian tunicate. It is commonly known as the star tunicate, but it also has several other common names, including star ascidian and golden star tunicate. Colonies grow on slow-moving, submerged objects, plants, and animals in nearshore saltwater environments.
Mastigias is a genus of true jellyfish in the family Mastigiidae. It contains seven described species. Members of this genus are found widely in coastal regions of the Indo-Pacific, including saline lakes of Palau, but there are also records from the West Atlantic at Florida and Puerto Rico. The West Atlantic records are most likely the result of accidental introductions by humans.
Corynactis californica is a brightly colored colonial anthozoan corallimorph. Unlike the Atlantic true sea anemone, Actinia fragacea, that bears the same common name, strawberry anemone, this species is a member of the order Corallimorpharia, and is the only member found in the North American West Coast. Other common names include club-tipped anemone and strawberry corallimorpharian. The anemone can live up to at least 50 meters deep on vertical rock walls, and at the bottom of kelp forests. It is known to carpet the bottom of some areas, like Campbell River in British Columbia, and Monterey Bay in California.
Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the Anemone, a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Hexacorallia. As cnidarians, sea anemones are related to corals, jellyfish, tube-dwelling anemones, and Hydra. Unlike jellyfish, sea anemones do not have a medusa stage in their life cycle.
Dromia personata, also known as the sponge crab or sleepy crab, is a species of crab found in the North Sea, the Mediterranean Sea, and connecting parts of the northeastern Atlantic Ocean. Like most other epibenthic crustaceans, the biomass of this species is especially dense in the Mediterranean continental shelf. It mainly resides from the lower shore to a depth of 50 meters (164 ft), often in caves. Occasionally, they are found living in depths as low as 110 meters (360 ft). They serve as prey for octopus, starfish, and other fish. Their last two pairs of legs are positioned dorsally, and are used to hold a sponge in place as camouflage.
Clavelina picta, common name the painted tunicate, is a species of tunicate, in the genus Clavelina. These animals, like all ascidians, are sessile filter feeders.
Berghia is a genus of sea slugs, aeolid nudibranchs. They are shell-less marine gastropod molluscs in the family Aeolidiidae. They are covered in cerata which give them their unique tentacle look and color. Berghia are commonly found in shallow waters and their diet consists of strictly Aiptasia Anemone. This genus is now commonly used commercially to fight off Anemone populations in fish tanks.
Convolutriloba is a genus of marine acoelomorph worms.
In biology, Gonozooids are any of the reproductive individuals of Tunicates, Bryozoan, or Hydrozoan colonies that produce gametes. Gonozooids may play a role in labour division or in alternation of generations. A gonozooid typically has hardly any other function than reproduction, amounting to little more than a motile gonad.
Nephromyces is a genus of apicomplexans that are symbionts of the ascidian genus Molgula.
Molgula occidentalis is a species of marine invertebrate of the family Molgulidae. The scientific name of the species was validated and published for the first time in 1883 by Traustedt. It is a soft-bodied, intertidal ascidian, sac-like filter feeders in the subphylum tunicate characterized by a hard outer covering known as a “tunic,” abundant in the shallow subtidal and intertidal zones of the Northern Gulf of Mexico, where they establish pseudopopulations.
Ophionereis schayeri, Schayer's brittle star, is a brittle star in the family Ophionereididae.
Echinaster is a well-studied and common genus of starfish containing ~30 species and is the second-largest genus found within the family Echinasteridae. The genera Henricia and Echinaster encompass 90% of all the species found within the family Echinasteridae. It contains 30 species, however the number of species in this genus is still debatable because of uncertainty within the genera. This genus is currently sub-divided into two sub-genera: Echinaster and Othilia, evolutionary relationships between the sub-genera is not understood. Echinaster are found in the Pacific, Atlantic and Indian oceans, with most species being studied in the Gulf of Mexico and Brazil. The sub-genera Othilia is thought to encompass species mainly found in the Gulf of Mexico and Brazil. Echinaster is often one of the most studied species within the family Echinasteridae and is often used to find evolutionary relationships.
References
- 1 2 Åkesson, Bertil; Robert Gschwentner; Jan Hendelberg; Peter Ladurner; Johann Müller; Reinhard Rieger (2001-12-01). "Fission in Convolutriloba longifissura: asexual reproduction in acoelous turbellarians revisited" (PDF). Acta Zoologica. 82 (3): 231–239. doi:10.1046/j.1463-6395.2001.00084.x. ISSN 1463-6395. Archived from the original (PDF) on 2016-03-04. Retrieved 2011-07-13.
- ↑ Egger, Bernhard (December 2008). "Regeneration: rewarding, but potentially risky" (PDF). Birth Defects Research Part C: Embryo Today: Reviews. 84 (4): 257–264. doi:10.1002/bdrc.20135. ISSN 1542-9768. PMID 19067421 . Retrieved 2011-07-13.
- 1 2 Herlant-Meewis, Henriette (1950-10-01). "Cyst-Formation in Aeolosoma Hemprichi (Ehr)". Biological Bulletin. 99 (2): 173–180. doi:10.2307/1538737. ISSN 0006-3185. JSTOR 1538737. PMID 14791418.
- ↑ Jaeckle, William B. (1994-02-01). "Multiple Modes of Asexual Reproduction by Tropical and Subtropical Sea Star Larvae: An Unusual Adaptation for Genet Dispersal and Survival". Biological Bulletin. 186 (1): 62–71. doi:10.2307/1542036. ISSN 0006-3185. JSTOR 1542036. PMID 29283296.
- ↑ Raikova, Ekaterina V. (1994-02-01). "Life Cycle, Cytology, and Morphology of Polypodium hydriforme, a Coelenterate Parasite of the Eggs of Acipenseriform Fishes". The Journal of Parasitology. 80 (1): 1–22. doi:10.2307/3283338. ISSN 0022-3395. JSTOR 3283338. PMID 7905920.