| Keratella cochlearis | |
|---|---|
 | |
| Kellicottia longispina and Keratella cochlearis | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Rotifera |
| Class: | Monogononta |
| Order: | Ploima |
| Family: | Brachionidae |
| Genus: | Keratella |
| Species: | K. cochlearis |
| Binomial name | |
| Keratella cochlearis | |
Keratella cochlearis is a rotifer. [2] The planktonic animal occurs worldwide in freshwater and marine habitats.
Keratella cochlearis has an oval lorica, a shell-like protective outer cuticle. At the anterior end are three pairs of spines. The central pair curve towards the ventral surface, the next pair diverge slightly and the outer pair converge. There is a single red eye [3] There is also a central funnel-shaped mouth and on either side of this are rings of cilia which twirl and help waft food particles into the mouth. They are also used for locomotion. There are two forms of this rotifer; some individuals have a long spine at the posterior end and others do not. Neither form has a foot. [4] [5]
Keratella cochlearis is found worldwide in marine, brackish and freshwater habitats. Any body of standing water is likely to contain rotifers and Keratella cochlearis is probably the most common and widespread species in the world. [5]
Keratella cochlearis is dioecious, with female specimens being larger than males. Typically, reproduction in this species is by parthenogenesis. In this process, the female rotifer produces an unfertilised egg with a full set of chromosomes. This is carried around by the mother and hatches into a miniature adult. Whether the offspring has a posterior spine or not seems to depend on the number of predators in the body of water where the rotifer lives. If predation rates are high, spined "typica" forms are produced, but if low, spineless forms known as "tecta" develop. Tecta females can produce typica offspring and vice versa. [4] It has also been found that different forms tend to predominate at different times of year. In the winter, most individuals have a long spine at the posterior end. As the spring advanced, the spine shortens and by July it is very short or non-existent. During the remaining months of the year it gradually lengthens once more. [5] These changes take place over several generations as each individual rotifer has a lifespan of just a few days or weeks. [6]
Periodically sexual reproduction takes place. It is not known why this occurs at some times and not others. The female undergoes meiosis and produces eggs with half the usual number of chromosomes. Some of these develop into male rotifers. Each of these is able to inseminate another of these eggs to restore the full complement of chromosomes in the offspring. [4]
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.
Sex is the trait that determines whether a sexually reproducing organism produces male or female gametes. Male plants and animals produce small mobile gametes, while females produce larger, non-motile ones. Organisms that produce both types of gametes are called hermaphrodites. During sexual reproduction, male and female gametes fuse to form zygotes, which develop into offspring that inherit traits from each parent.
The gastrotrichs, commonly referred to as hairybellies or hairybacks, are a group of microscopic (0.06-3.0 mm), cylindrical, acoelomate animals, and are widely distributed and abundant in freshwater and marine environments. They are mostly benthic and live within the periphyton, the layer of tiny organisms and detritus that is found on the seabed and the beds of other water bodies. The majority live on and between particles of sediment or on other submerged surfaces, but a few species are terrestrial and live on land in the film of water surrounding grains of soil. Gastrotrichs are divided into two orders, the Macrodasyida which are marine, and the Chaetonotida, some of which are marine and some freshwater. Nearly 800 species of gastrotrich have been described.
The rotifers, commonly called wheel animals or wheel animalcules, make up a phylum of microscopic and near-microscopic pseudocoelomate animals.
Daphnia is a genus of small planktonic crustaceans, 0.2–6.0 mm (0.01–0.24 in) in length. Daphnia are members of the order Anomopoda, and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory swimming style resembles the movements of fleas. Daphnia spp. live in various aquatic environments ranging from acidic swamps to freshwater lakes and ponds.
Bdelloidea is a class of rotifers found in freshwater habitats all over the world. There are over 450 described species of bdelloid rotifers, distinguished from each other mainly on the basis of morphology. The main characteristics that distinguish bdelloids from related groups of rotifers are exclusively parthenogenetic reproduction and the ability to survive in dry, harsh environments by entering a state of desiccation-induced dormancy (anhydrobiosis) at any life stage. They are often referred to as "ancient asexuals" due to their unique asexual history that spans back to over 25 million years ago through fossil evidence. Bdelloid rotifers are microscopic organisms, typically between 150 and 700 µm in length. Most are slightly too small to be seen with the naked eye, but appear as tiny white dots through even a weak hand lens, especially in bright light. In June 2021, biologists reported the restoration of bdelloid rotifers after being frozen for 24,000 years in the Siberian permafrost.
Monogononta is a class of rotifers, found mostly in freshwater but also in soil and marine environments. They include both free-swimming and sessile forms. Monogononts generally have a reduced corona, and each individual has a single gonad, which gives the group its name. Males are generally smaller than females, and are produced only during certain times of the year, with females otherwise reproducing through parthenogenesis.
The sticklebacks are a family of ray-finned fishes, the Gasterosteidae which have a Holarctic distribution in fresh, brackish and marine waters. They were thought to be related to the pipefish and seahorses but are now thought to be more closely related to the eelpouts and sculpins.
The three-spined stickleback is a fish native to most inland and coastal waters north of 30°N. It has long been a subject of scientific study for many reasons. It shows great morphological variation throughout its range, ideal for questions about evolution and population genetics. Many populations are anadromous and very tolerant of changes in salinity, a subject of interest to physiologists. It displays elaborate breeding behavior and it can be social making it a popular subject of inquiry in fish ethology and behavioral ecology. Its antipredator adaptations, host-parasite interactions, sensory physiology, reproductive physiology, and endocrinology have also been much studied. Facilitating these studies is the fact that the three-spined stickleback is easy to find in nature and easy to keep in aquaria.
Haplodiploidy is a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid. Haplodiploidy is sometimes called arrhenotoky.
The Banggai cardinalfish is a small tropical cardinalfish in the family Apogonidae. It is the only member of its genus. This attractive fish is popular in the aquarium trade. It is among the relatively few marine fish to have been bred regularly in captivity, but significant numbers are still captured in the wild and it is now an endangered species. The detrimental impact of humans on its environment and certain fatal diseases threaten this species' numbers significantly. Iridovirus diseases are known to be significant reason for fish mortality.
Parthenogenesis is a natural form of asexual reproduction in which growth and development of embryos occur in a gamete without combining with another gamete. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.
Brachionus is a genus of planktonic rotifers occurring in freshwater, alkaline and brackish water.
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.
The reproductive system of gastropods varies greatly from one group to another within this very large and diverse taxonomic class of animals. Their reproductive strategies also vary greatly, see Mating of gastropods.
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.
Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all-female populations reproduce without the involvement of males, are found in squamate reptiles. There are about 50 species of lizard and 1 species of snake that reproduce solely through parthenogenesis. It is unknown how many sexually reproducing species are also capable of parthenogenesis in the absence of males, but recent research has revealed that this ability is widespread among squamates.
Elacatinus colini, the Belize sponge goby, is a species of goby native to the Western Central Atlantic Ocean, near Belize and Honduras.
Brachionidae is a family of rotifers belonging to the order Ploima. Species are found in freshwater and marine habitats.
Androgenesis occurs when a zygote is produced with only paternal nuclear genes. During standard sexual reproduction, one female and one male parent each produce haploid gametes, which recombine to create offspring with genetic material from both parents. However, in androgenesis, there is no recombination of maternal and paternal chromosomes, and only the paternal chromosomes are passed down to the offspring. The offspring produced in androgenesis will still have maternally inherited mitochondria, as is the case with most sexually reproducing species.