Hydra viridissima | |
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Hydra viridissima | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Cnidaria |
Class: | Hydrozoa |
Order: | Anthoathecata |
Family: | Hydridae |
Genus: | Hydra |
Species: | H. viridissima |
Binomial name | |
Hydra viridissima | |
Synonyms | |
Hydra viridissima is a species of cnidarian which is commonly found in still or slow-moving freshwater [2] in the Northern temperate zone. Hydra viridissima is commonly called green hydra due to its coloration, which is due to the symbiotic green algae Chlorella vulgaris which live within its body. [3] These creatures are typically 10 mm long and have tentacles that are about half of their length. [4] They are strictly carnivorous and typically feed on small crustaceans, insects and annelids. Hydra are normally sessile and live on aquatic vegetation. They secrete mucous to attach to substrate using their basal disc. [4]
Hydra are multi-cellular organisms. They are made up of two layers of epithelial cells and have a hypostome or mouth opening. Circling the mouth are tentacles that contain nematocysts or stinging cells to help in prey capture. The mouth and tentacles are called the hydranth. The rest of the Hydra is known as the column and is divided into four sections: the gastric section (between the tentacles and first bud), budding section (which produces the buds), the peduncle (between the lowest bud and basal disc), and the basal disc (foot-like structure). Hydra are diploblastic organisms, the body is composed of two embryonic cell layers; the ectoderm and the endoderm. The endoderm lines the gastrovascular cavity, which is a water-filled sac, this acts as a hydroskeleton and site for food digestion. They also have a simple nervous system that consist of a nerve net that covers the entire body. [5]
Although Hydra are sessile, they can move in short bursts. An individual can extend and contract with a mixture of muscle movement and water (hydraulic) pressure created inside the digestive cavity. Tiny cells that line the digestive system possess flagella which create a current to draw water into the digestive cavity. These cells can extend the length of the body column. They can detach their basal disc from the substrate and move to a new location by gliding or by "somersaulting", which they do by detaching the disc then bending over and over using the tentacles to push over when they rotate around. Individuals may repeat attaching and detaching many times until they find a desirable location. Hydra can also move by floating upside down using a gas bubble produced on the basal disc which carries the creature to the water surface. [6]
H. viridissima is currently the only known Hydra species that has a permanent symbiotic relationship with photosynthetic unicellular Chlorella algae. These algae are located in the endodermal epithelial cells which are enclosed by an individual vacuolar membrane, which enclose inorganic and organic molecules for storage. [7] The endodermal epithelium is composed of many cells, each housing 20–40 individual algae organisms. [8] The algae supply nutrients produced via photosynthesis to the Hydra. Because the algae live in the vacuoles of the cells, they are protected from the digestive enzymes of the Hydra. [3] During long period of darkness, such as storms or blooms that block sunlight, algae loss starts from the tentacles, hypostome and growth region. When light conditions return, the algae undergo rapid multiplication and can repopulate the host in approximately two days. [9] Chlorella undergo asexual reproduction which is in correlation with the division of the host. [8] The Hydra regulates the population of the Chlorella algae by digesting excess algae or controlling algal cell division. [10]
Hydra are capable of escaping death by renewing their body tissues. Mortality rates are extremely low and there have been no signs of decline in reproductive rate. [11]
Hydra cannot be found in impaired water due to their low tolerance to pollution. They can be used to rank toxicants on level of potential hazard. The simple tubular body and diploblastic membranes, all of the epithelial cells are in constant contact with the environment, this allows for toxic substances being exposed to all body surface. [5] Harsh metals and high levels of those metals can cause mortality. One advantage of being able to reproduce asexually is that they can still reproduce successfully during times where there are high levels of harsh metals. [12]
Hydra are typically hermaphroditic or gonochoric. Uniquely to Hydra, the medusa stage is absent and only the polyps will reproduce sexually and asexually. [2] H. viridissima will reproduce sexually when temperatures have warmed to at least 20 °C, typically this falls between May and June. Larger individuals will produce both ovaries and testes, while smaller individuals only develop testicles. Sexual reproduction can be seen as a strategy to survive during times of low nutrients and other unfavorable conditions. H. viridissima has three sexes: female, male, and hermaphrodite. Simultaneous hermaphrodites are dominant during the growing season. It is thought that female gonads need a longer period of inductive conditions for production, that means that there is a scarcity of females in most populations. During the summer months, specifically in Poland Lemna bloom occurs that reduces light attenuation which reduces photosynthesis efficiency of the Chlorella algae, this influences the asexual behavior. Even though during the beginning of the mating season for the Hydra, all the individuals are sexually active, asexual reproduction is a main strategy for reproduction. This behavior of interference of asexual and sexual reproduction allows population growth to continue throughout all conditions. [13]
When the Hydra reproduces asexually, buds will be produced that attach to the body wall. The buds are genetically identical clones of the parent. When they are mature they will break free. The parent can possess several buds that are at different stages of development at the same time. The bud once detached from the parent will float until they find some hard substrate to attach to. [2]
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. 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.
The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some green algae may store food in the form of oil droplets. They usually have a cell wall made up of an inner layer of cellulose and outer layer of pectose.
Cnidaria is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Hydra is a genus of small, freshwater organisms of the phylum Cnidaria and class Hydrozoa. They are native to the temperate and tropical regions. The genus was named by Linnaeus in 1758 after the Hydra, which was the many-headed beast defeated by Hercules as when the animal had a part severed, it would regenerate much like the hydra’s heads. Biologists are especially interested in Hydra because of their regenerative ability; they do not appear to die of old age, or to age at all.
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.
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral end is attached to the substrate by means of a disc-like holdfast called a pedal disc, while in colonies of polyps it is connected to other polyps, either directly or indirectly. The oral end contains the mouth, and is surrounded by a circlet of tentacles.
Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is known as a bud. Since the reproduction is asexual, the newly created organism is a clone and excepting mutations is genetically identical to the parent organism. Organisms such as hydra use regenerative cells for reproduction in the process of budding.
Biological immortality is a state in which the rate of mortality from senescence is stable or decreasing, thus decoupling it from chronological age. Various unicellular and multicellular species, including some vertebrates, achieve this state either throughout their existence or after living long enough. A biologically immortal living being can still die from means other than senescence, such as through injury, poison, disease, lack of available resources, or changes to environment.
Hydra oligactis, also known as the brown hydra, is a species of hydra found widely dispersed in the northern temperate zone. It is a common organism found in still waters from early Spring to late Autumn.
Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.
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.
Aiptasia is a genus of a symbiotic cnidarian belonging to the class Anthozoa. Aiptasia is a widely distributed genus of temperate and tropical sea anemones of benthic lifestyle typically found living on mangrove roots and hard substrates. These anemones, as well as many other cnidarian species, often contain symbiotic dinoflagellate unicellular algae of the genus Symbiodinium living inside nutritive cells. The symbionts provide food mainly in the form of lipids and sugars produced from photosynthesis to the host while the hosts provides inorganic nutrients and a constant and protective environment to the algae. Species of Aiptasia are relatively weedy anemones able to withstand a relatively wide range of salinities and other water quality conditions. In the case of A. pallida and A. pulchella, their hardiness coupled with their ability to reproduce very quickly and out-compete other species in culture gives these anemones the status of pest from the perspective of coral reef aquarium hobbyists. These very characteristics make them easy to grow in the laboratory and thus they are extensively used as model organisms for scientific study. In this respect, Aiptasia have contributed a significant amount of knowledge regarding cnidarian biology, especially human understanding of cnidarian-algal symbioses, a biological phenomenon crucial to the survival of corals and coral reef ecosystems. The dependence of coral reefs on the health of the symbiosis is dramatically illustrated by the devastating effects experienced by corals due to the loss of algal symbionts in response to environmental stress, a phenomenon known as coral bleaching.
Entomophthora is a fungal genus in the family Entomophthoraceae. Species in this genus are parasitic on flies and other two-winged insects. The genus was circumscribed by German biologist Ferdinand Cohn in 1856.
Sea anemones are a group of predatory marine animals 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.
Hydra vulgaris, the fresh-water polyp, is a small animal freshwater hydroid with length from 10 mm to 30 mm and width about 1 mm.
Convolutriloba is a genus of marine acoelomorph worms.
Aiptasia diaphana, commonly known as the yellow aiptasia or glasrose, is a species of sea anemone native to shallow waters in the temperate eastern Atlantic Ocean and the Mediterranean Sea. It has been introduced into the Red Sea.
The Enthemonae is a suborder of sea anemones in the order Actiniaria. It comprises those sea anemones with typical arrangement of mesenteries for actiniarians.
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.
Clava is a monotypic genus of hydrozoans in the family Hydractiniidae. It contains only one accepted species, Clava multicornis. Other names synonymous with Clava multicornis include Clava cornea, Clava diffusa, Clava leptostyla, Clava nodosa, Clava parasitica, Clava squamata, Coryne squamata, Hydra multicornis, and Hydra squamata. The larvae form of the species has a well developed nervous system compared to its small size. The adult form is also advanced due to its ability to stay dormant during unfavorable periods.