The lion is a species in the family Felidae. The lion is sexually dimorphic. Male lions have a prominent mane, the most recognisable feature of the species. A lion pride consists of related females and cubs. Groups of female lions hunt together, preying on large ungulates; the species is an keystone predator, although they scavenge when opportunities occur. Some lions have been known to hunt humans, although the species does not; the lion inhabits grasslands and savannas but is absent in dense forests. It is more diurnal than other big cats, but when persecuted it adapts to being active at night and at twilight. In the Pleistocene, the lion ranged throughout Eurasia and North America but today it has been reduced to fragmented populations in Sub-Saharan Africa and one critically endangered population in western India, it has been listed as Vulnerable on the IUCN Red List since 1996 because populations in African countries have declined by about 43% since the early 1990s. Lion populations are untenable outside designated protected areas.
Although the cause of the decline is not understood, habitat loss and conflicts with humans are the greatest causes for concern. One of the most recognised animal symbols in human culture, the lion has been extensively depicted in sculptures and paintings, on national flags, in contemporary films and literature. Lions have been kept in menageries since the time of the Roman Empire and have been a key species sought for exhibition in zoological gardens across the world since the late 18th century. Cultural depictions of lions were prominent in the Upper Paleolithic period; the lion's name, similar in many Romance languages, is derived from Latin: leo and Ancient Greek: λέων. The word lavi may be related. Felis leo was the scientific name used by Carl Linnaeus in 1758, who described the lion in his work Systema Naturae; the genus name Panthera was coined by German naturalist Lorenz Oken in 1816. Between the mid-18th and mid-20th centuries, 26 lion specimens were described and proposed as subspecies, of which 11 were recognised as valid in 2005.
They were distinguished on the basis of appearance and colour of mane. Because these characteristics show much variation between individuals, most of these forms were not true subspecies because they were based upon museum material with "striking, but abnormal" morphological characteristics. Based on the morphology of 58 lion skulls in three European museums, the subspecies krugeri, nubica and senegalensis were assessed distinct but bleyenberghi overlapped with senegalensis and krugeri; the Asiatic lion persica was the most distinctive and the Cape lion had characteristics allying it more with persica than the other sub-Saharan lions. The lion's closest relatives are the other species of the genus Panthera. Results of phylogenetic studies published in 2006 and 2009 indicate that the jaguar and the lion belong to one sister group that diverged about 2.06 million years ago. Results of studies published in 2010 and 2011 indicate that the leopard and the lion belong to the same sister group, which diverged between 1.95 and 3.10 million years ago.
Hybridisation between lion and snow leopard ancestors, may have continued until about 2.1 million years ago. In the 19th and 20th centuries, several lion type specimens were described and proposed as subspecies, with about a dozen recognised as valid taxa until 2017. Between 2008 and 2016, IUCN Red List assessors used only two subspecific names: P. l. leo for African lion populations and P. l. persica for the Asiatic lion population. In 2017, the Cat Classification Task Force of the Cat Specialist Group revised lion taxonomy, recognises two subspecies based on results of several phylogeographic studies on lion evolution, namely: P. l. leo − the nominate lion subspecies includes the Asiatic lion, the regionally extinct Barbary lion, lion populations in West and northern parts of Central Africa. Synonyms include P. l. persica, P. l. senegalensis, P. l. kamptzi, P. l. azandica. Some authors referred to it as'Northern lion' and'northern subspecies'. P. l. melanochaita − includes the extinct Cape lion and lion populations in East and Southern African regions.
Synonyms include P. l. somaliensis, P. l. massaica, P. l. sabakiensis, P. l. bleyenberghi, P. l. roosevelti, P. l. nyanzae, P. l. hollisteri, P. l. krugeri, P. l. vernayi, P. l. webbiensis. It has been referred to as'southern subspecies'. Early phylogenetic research was focused on East and Southern African lions, showed they can be divided in two main clades. Lions in eastern Kenya are genetically much closer to lions in Southern Africa than to lions in Aberdare National Park in western Kenya. In a subsequent study and bone samples of 32 lion specimens in museums were used. Results indicated lions form
Novomessor cockerelli is a species of ant in the subfamily Myrmicinae. It is native to the deserts of the Southwestern United States and Mexico, it lives in large underground colonies. The worker ants leave the nest daily to forage for plant material and dead insects. Novomessor cockerelli is a large brown ant with long legs and an elongated head, it can be recognised by the two distinctive spines on the propodeum. It can be distinguished from the rather similar Aphaenogaster albisetosa by the shape of its head, it cannot sting but is aggressive and has a powerful bite. Novomessor cockerelli is found in arid areas of the Southwestern United States including Texas and the Franklin Mountains, New Mexico, Arizona and California, it is present in northern Mexico in the states of Sonora, Durango and Nuevo León. Its typical habitat is upland plains includes desert areas with ocotillo, creosote bush, mesquite and thorn scrub at altitudes of between 518 and 1,877 m above sea level. Novomessor cockerelli forms large underground colonies, sometimes with multiple entrances, on open ground or beside rocks.
The nest tends to be surrounded by a midden, a circle of tiny pebbles and plant remains. The worker ants leave the nest to forage in the early morning and in the evening, at which times the ground temperature is within the range 20 to 40 °C. During the winter they may forage throughout the day. Seeds and plant material are collected but nearly half of the diet consists of the corpses of insects; these ants scavenge around carcases for dead insects such as flies. When a prey item is found, too large for a single ant to carry, other ants are recruited by the use of pheromones; the original ant liberates a glandular secretion which attracts other workers within about two metres of the release point. If this fails to summon enough assistance, it releases a further secretion on the ground and lays a trail back to the colony. Other ants are attracted to follow the trail and work co-operatively to transport the food item back to the nest; the trail is short-lived and soon evaporates. In the Chihuahuan Desert, Novomessor cockerelli competes for resources with another seed-eating ant species, the red harvester ant.
It has been found that workers of N. cockerelli will emerge from the nest early in the morning and plug the entrance holes of nearby P. barbatus colonies with grit and small stones thus delaying the emergence of the other workers. Nests close to the A. cockerelli home nest are plugged more than ones far away, older, larger nests have their entrances plugged more than younger, smaller ones. In the Chihuahuan Desert, nuptial flights of Novomessor cockerelli occur in July at dusk. After returning to the ground, newly mated females soon remove their wings, they are not permitted by workers to enter established nests, but must found a new colony on their own. Each colony contains a single queen, she uses bodily secretions to prevent other colony members from laying viable eggs. The workers spend little time licking or grooming the queen and it is unclear how her control of the colony comes about, it may be related to the coating of the eggs she lays, because the workers which care for them do lick them.
The queen has a gland called the Dufour’s gland which secretes a chemical that she uses to mark any reproductive workers that may be present in the nest. This causes other worker ants to attack the marked ants and helps her maintain her dominant position. In an established colony, workers do not regurgitate food to give to the queen but instead lay trophic eggs for her to eat, these eggs are fed to the queen larvae. Workers seem to have alternating periods when they either go out to forage or they stay in the nest and tend the brood, at which time they are capable of producing trophic eggs. In a colony, deprived of its queen, some of the workers begin to lay and tend viable eggs after a few weeks, these all develop into males; the colony ceases to exist when the males have emerged and all the workers have come to the end of their lives. Media related to Novomessor cockerelli at Wikimedia Commons
In ethology, territory is the sociographical area that an animal of a particular species defends against conspecifics. Animals that defend territories in this way are referred to as territorial. Territoriality is only shown by a minority of species. More an individual or a group of animals has an area that it habitually uses but does not defend; the home ranges of different groups of animals overlap, or in the overlap areas, the groups tend to avoid each other rather than seeking to expel each other. Within the home range there may be a core area that no other individual group uses, again, this is as a result of avoidance; the ultimate function of animals inhabiting and defending a territory is to increase the individual fitness or inclusive fitness of the animals expressing the behaviour. Fitness in this biological sense relates to the ability of an animal to raise young; the proximate functions of territory defense vary. For some animals, the reason for such protective behaviour is to acquire and protect food sources, nesting sites, mating areas, or to attract a mate.
Among birds, territories have been classified as six types. Type A: An'all-purpose territory' in which all activities occur, e.g. courtship, mating and foraging Type B: A mating and nesting territory, not including most of the area used for foraging. Type C: A nesting territory which includes the nest plus a small area around it. Common in colonial waterbirds. Type D: A pairing and mating territory; the type of territory defended by males in lekking species. Type E: Roosting territory. Type F: Winter territory which includes foraging areas and roost sites. May be equivalent to the Type A territory, or for a migratory species, may be on the wintering grounds. Reports of territory size can be confused by a lack of distinction between home range and the defended territory; the size and shape of a territory can vary according to its purpose, the amount and quality of resources it contains, or the geography. The size is a compromise of resource needs, defense costs, predation pressure and reproductive needs.
Some species of squirrels may claim as much as 10 hectares of territory. For European badgers, a home range may be as small as 30 hectares in a good rural habitat, but as large as 300 hectares in a poor habitat. On average, a territory may be 50 hectares, with main setts at least 500 metres apart. In urban areas, territories can be as small as 5 hectares, if they can obtain enough food from bird tables, food waste or artificial feeding in suburban gardens. Spotted hyenas have variable territory sizes, ranging from less than 4,000 hectares in the Ngorongoro Crater to over 100,000 hectares in the Kalahari. In birds, golden eagles have territories of 9,000 hectares, least flycatchers' territories are about 600 square metres and gulls have territories of only a few square centimetres in the immediate vicinity of the nest. Territories can be linear. Sanderlings forage on sandflats; when on beaches, they feed either in flocks or individual territories of 10 to 120 metres of shoreline. The time to develop territories varies between animals.
The marine iguana is a lekking reptile. Males start to establish small display territories two months ahead of the mating season. Rather than retaining a territory by fighting, for some animals this can be a 3-stage process. Many animals create "sign-posts" to advertise their territory. Sometimes these sign-posts are on the boundary thereby demarcating the territory, or, may be scattered throughout the territory; these communicate to other animals that the territory is occupied and may communicate additional information such as the sex, reproductive status or dominance status of the territory-holder. Sign-posts may communicate information by olfactory, auditory, or visual means, or a combination of these. If an intruder progresses further into the territory beyond the sign-posts and encounters the territory-holder, both animals may begin ritualized aggression toward each other; this is a series of stylised postures, displays, etc. which function to solve the territory dispute without actual fighting as this could injure either or both animals.
Ritualized aggression ends by one of the animals fleeing. If this does not happen, the territory may be defended by actual fighting, although this is a last resort. Scent marking known as territorial marking or spraying when this involves urination, is a behaviour used by animals to identify their territory. Most this is accomplished by depositing strong-smelling substances contained in the urine, faeces, or, from specialised scent glands located on various areas of the body; the scent contains pheromones or carrier proteins such as the major urinary proteins to stabilize the odours and maintain them for longer. The animal sniffing the scent displays a flehmen response to assist in detecting the mark. Scent marking is performed by scent rubbing in many mammals. In many mammal species, scent marking is more frequent during the breeding season. Felids such as leopards and jaguars mark by rubbing themselves against vegetation. Fraser, Andrew Ferguson. Feline Behaviour and Welfare. CABI. p. 53. ISBN 9781845939267.
Prosimians and New World monkeys use scent marking, including urine washing, to communicate. Many ungulates, for example the blue wildebeest, use scent marking from two glands, the preorbital gland and a scent gland in the hoof. Territorial scent marking
Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resources in an ecosystem. This can be contrasted with a type of symbiosis. Competition between members of the same species is called intraspecific competition. If a tree species in a dense forest grows taller than surrounding tree species, it is able to absorb more of the incoming sunlight. However, less sunlight is available for the trees that are shaded by the taller tree, thus interspecific competition. Leopards and lions can be in interspecific competition, since both species feed on the same prey, can be negatively impacted by the presence of the other because they will have less food. Competition is only one of many interacting biotic and abiotic factors that affect community structure. Moreover, competition is not always a straightforward, interaction. Interspecific competition may occur when individuals of two separate species share a limiting resource in the same area.
If the resource cannot support both populations lowered fecundity, growth, or survival may result in at least one species. Interspecific competition has the potential to alter populations and the evolution of interacting species. On an individual organism level, competition can occur as exploitative competition. Direct competition has been observed between individuals and species, but there is little evidence that competition has been the driving force in the evolution of large groups. For example, between amphibians and mammals. All of the types described here can apply to intraspecific competition, that is, competition among individuals within a species. Any specific example of interspecific competition can be described in terms of both a mechanism and an outcome. Exploitative competition referred to as resource competition, is a form of competition in which one species consumes and either reduces or more efficiently uses a shared limiting resource and therefore depletes the availability of the resource for the other species.
Thus, it is an indirect interaction because the competing species interact via a shared resource. Interference competition is a form of competition in which individuals of one species interacts directly with individuals of another species via antagonistic displays or more aggressive behavior. In a review and synthesis of experimental evidence regarding interspecific competition, Schoener described six specific types of mechanisms by which competition occurs, including consumptive, overgrowth, chemical and encounter. Consumption competition is always resource competition, but the others are cannot always be regarded as exploitative or interference. Separating the effect of resource use from that of interference is not easy. A good example of exploitative competition is found in aphid species competing over the sap in plant phloem; each aphid species that feeds on host plant sap uses some of the resource, leaving less for competing species. In one study, Fordinae geoica was observed to out-compete F. formicaria to the extent that the latter species exhibited a reduction in survival by 84%.
Another example is the one of competition for calling space in amphibians, where the calling activity of a species prevents the other one from calling in an area as wide as it would in allopatry. A last example is driving of bisexual rock lizards of genus Darevskia from their natural habitats by a daughter unisexual form; this type of competition can be observed in forests where large trees dominate the canopy and thus allow little light to reach smaller competitors living below. These interactions have important implications for the population dynamics and distribution of both species. Scramble and contest competition refer to the relative success of competitors. Scramble competition is said to occur when each competitor is equal suppressed, either through reduction in survival or birth rates. Contest competition is said to occur when one or a few competitors are unaffected by competition, but all others suffer either through reduction in survival or birth rates. Sometimes these types of competition are referred to as symmetric vs. asymmetric competition.
Scramble and contest competition are two ends of a spectrum, of equal or unequal effects. Apparent competition is an example of predation that alters the relative abundances of prey on the same trophic level, it occurs when two or more species in a habitat affect shared natural enemies in a higher trophic level. If two species share a common predator, for example, apparent competition can exist between the two prey items in which the presence of each prey species increases the abundance of the shared enemy, thereby suppresses one or both prey species; this mechanism gets its name from experiments in which one prey species is removed and the second prey species increases in abundance. Investigators sometimes mistakenly attribute the increase in abundance in the second species as evidence for resource competition between prey species, it is "apparently" competition, but is in fact due to a shared predator, parasite, or pathogen. Many studies, including those cited have shown major impacts on both individuals and populations from interspecific competition.
Documentation of these impacts has been found in species from every major branch of organism. The effects of interspecific competition can reach communities and can influence the evolution of spec
In biology, an organism is any individual entity that exhibits the properties of life. It is a synonym for "life form". Organisms are classified by taxonomy into specified groups such as the multicellular animals and fungi. All types of organisms are capable of reproduction and development, some degree of response to stimuli. Humans are multicellular animals composed of many trillions of cells which differentiate during development into specialized tissues and organs. An organism may be either a eukaryote. Prokaryotes are represented by two separate domains -- archaea. Eukaryotic organisms are characterized by the presence of a membrane-bound cell nucleus and contain additional membrane-bound compartments called organelles. Fungi and plants are examples of kingdoms of organisms within the eukaryotes. Estimates on the number of Earth's current species range from 10 million to 14 million, of which only about 1.2 million have been documented. More than 99% of all species, amounting to over five billion species, that lived are estimated to be extinct.
In 2016, a set of 355 genes from the last universal common ancestor of all organisms was identified. The term "organism" first appeared in the English language in 1703 and took on its current definition by 1834, it is directly related to the term "organization". There is a long tradition of defining organisms as self-organizing beings, going back at least to Immanuel Kant's 1790 Critique of Judgment. An organism may be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. Dictionary definitions can be broad, using phrases such as "any living structure, such as a plant, fungus or bacterium, capable of growth and reproduction". Many definitions exclude viruses and possible man-made non-organic life forms, as viruses are dependent on the biochemical machinery of a host cell for reproduction. A superorganism is an organism consisting of many individuals working together as a single functional or social unit. There has been controversy about the best way to define the organism and indeed about whether or not such a definition is necessary.
Several contributions are responses to the suggestion that the category of "organism" may well not be adequate in biology. Viruses are not considered to be organisms because they are incapable of autonomous reproduction, growth or metabolism; this controversy is problematic because some cellular organisms are incapable of independent survival and live as obligatory intracellular parasites. Although viruses have a few enzymes and molecules characteristic of living organisms, they have no metabolism of their own; this rules out autonomous reproduction: they can only be passively replicated by the machinery of the host cell. In this sense, they are similar to inanimate matter. While viruses sustain no independent metabolism and thus are not classified as organisms, they do have their own genes, they do evolve by mechanisms similar to the evolutionary mechanisms of organisms; the most common argument in support of viruses as living organisms is their ability to undergo evolution and replicate through self-assembly.
Some scientists argue. In fact, viruses are evolved by their host cells, meaning that there was co-evolution of viruses and host cells. If host cells did not exist, viral evolution would be impossible; this is not true for cells. If viruses did not exist, the direction of cellular evolution could be different, but cells would be able to evolve; as for the reproduction, viruses rely on hosts' machinery to replicate. The discovery of viral metagenomes with genes coding for energy metabolism and protein synthesis fueled the debate about whether viruses belong in the tree of life; the presence of these genes suggested. However, it was found that the genes coding for energy and protein metabolism have a cellular origin. Most these genes were acquired through horizontal gene transfer from viral hosts. Organisms are complex chemical systems, organized in ways that promote reproduction and some measure of sustainability or survival; the same laws that govern non-living chemistry govern the chemical processes of life.
It is the phenomena of entire organisms that determine their fitness to an environment and therefore the survivability of their DNA-based genes. Organisms owe their origin and many other internal functions to chemical phenomena the chemistry of large organic molecules. Organisms are complex systems of chemical compounds that, through interaction and environment, play a wide variety of roles. Organisms are semi-closed chemical systems. Although they are individual units of life, they are not closed to the environment around them. To operate they take in and release energy. Autotrophs produce usable energy using light from the sun or inorganic compounds while heterotrophs take in organic compounds from the environment; the primary chemical element in these compounds is carbon. The chemical properties of this element such as its grea
Ecology is the branch of biology which studies the interactions among organisms and their environment. Objects of study include interactions of organisms that include biotic and abiotic components of their environment. Topics of interest include the biodiversity, distribution and populations of organisms, as well as cooperation and competition within and between species. Ecosystems are dynamically interacting systems of organisms, the communities they make up, the non-living components of their environment. Ecosystem processes, such as primary production, nutrient cycling, niche construction, regulate the flux of energy and matter through an environment; these processes are sustained by organisms with specific life history traits. Biodiversity means the varieties of species and ecosystems, enhances certain ecosystem services. Ecology is not synonymous with natural history, or environmental science, it overlaps with the related sciences of evolutionary biology and ethology. An important focus for ecologists is to improve the understanding of how biodiversity affects ecological function.
Ecologists seek to explain: Life processes and adaptations The movement of materials and energy through living communities The successional development of ecosystems The abundance and distribution of organisms and biodiversity in the context of the environment. Ecology has practical applications in conservation biology, wetland management, natural resource management, city planning, community health, economics and applied science, human social interaction. For example, the Circles of Sustainability approach treats ecology as more than the environment'out there', it is not treated as separate from humans. Organisms and resources compose ecosystems which, in turn, maintain biophysical feedback mechanisms that moderate processes acting on living and non-living components of the planet. Ecosystems sustain life-supporting functions and produce natural capital like biomass production, the regulation of climate, global biogeochemical cycles, water filtration, soil formation, erosion control, flood protection, many other natural features of scientific, economic, or intrinsic value.
The word "ecology" was coined in 1866 by the German scientist Ernst Haeckel. Ecological thought is derivative of established currents in philosophy from ethics and politics. Ancient Greek philosophers such as Hippocrates and Aristotle laid the foundations of ecology in their studies on natural history. Modern ecology became a much more rigorous science in the late 19th century. Evolutionary concepts relating to adaptation and natural selection became the cornerstones of modern ecological theory; the scope of ecology contains a wide array of interacting levels of organization spanning micro-level to a planetary scale phenomena. Ecosystems, for example, contain interacting life forms. Ecosystems are dynamic, they do not always follow a linear successional path, but they are always changing and sometimes so that it can take thousands of years for ecological processes to bring about certain successional stages of a forest. An ecosystem's area can vary from tiny to vast. A single tree is of little consequence to the classification of a forest ecosystem, but critically relevant to organisms living in and on it.
Several generations of an aphid population can exist over the lifespan of a single leaf. Each of those aphids, in turn, support diverse bacterial communities; the nature of connections in ecological communities cannot be explained by knowing the details of each species in isolation, because the emergent pattern is neither revealed nor predicted until the ecosystem is studied as an integrated whole. Some ecological principles, however, do exhibit collective properties where the sum of the components explain the properties of the whole, such as birth rates of a population being equal to the sum of individual births over a designated time frame; the main subdisciplines of ecology, population ecology and ecosystem ecology, exhibit a difference not only of scale, but of two contrasting paradigms in the field. The former focus on organisms distribution and abundance, while the focus on materials and energy fluxes; the scale of ecological dynamics can operate like a closed system, such as aphids migrating on a single tree, while at the same time remain open with regard to broader scale influences, such as atmosphere or climate.
Hence, ecologists classify ecosystems hierarchically by analyzing data collected from finer scale units, such as vegetation associations and soil types, integrate this information to identify emergent patterns of uniform organization and processes that operate on local to regional and chronological scales. To structure the study of ecology into a conceptually manageable framework, the biological world is organized into a nested hierarchy, ranging in scale from genes, to cells, to tissues, to organs, to organisms, to species, to populations, to communities, to ecosystems, to biomes, up to the level of the biosphere; this framework exhibits non-linear behaviors.
Sea anemones are a group of marine, predatory animals of the order Actiniaria. They are named after the anemone, a terrestrial flowering plant, because of the colourful appearance of many. Sea anemones are classified in the phylum class Anthozoa, subclass Hexacorallia; as cnidarians, sea anemones are related to corals, tube-dwelling anemones, Hydra. Unlike jellyfish, sea anemones do not have a medusa stage in their life cycle. A typical sea anemone is a single polyp attached to a hard surface by its base, but some species live in soft sediment and a few float near the surface of the water; the polyp has a columnar trunk topped by an oral disc with a ring of a central mouth. The tentacles can be expanded to catch passing prey, they are armed with cnidocytes. In many species, additional nourishment comes from a symbiotic relationship with single-celled dinoflagellates, zooxanthellae or with green algae, that live within the cells; some species of sea anemone live in association with hermit crabs, small fish or other animals to their mutual benefit.
Sea anemones breed by liberating sperm and eggs through the mouth into the sea. The resulting fertilized eggs develop into planula larvae which, after being planktonic for a while, settle on the seabed and develop directly into juvenile polyps. Sea anemones breed asexually, by breaking in half or into smaller pieces which regenerate into polyps. Sea anemones are sometimes kept in reef aquariums. A typical sea anemone is a sessile polyp attached at the base to the surface beneath it by an adhesive foot, called a basal or pedal disc, with a column-shaped body topped by an oral disc. Most are from 1 to 5 cm in diameter and 1.5 to 10 cm in length, but they are inflatable and vary in dimensions. Some are large; some species burrow in soft sediment and lack a basal disc, having instead a bulbous lower end, the physa, which anchors them in place. The column or trunk is more or less cylindrical and may be plain and smooth or may bear specialist structures. In some species the part below the oral disc is constricted and is known as the capitulum.
When the animal contracts, the oral disc and capitulum fold inside the pharynx and are held in place by a strong sphincter muscle part way up the column. There may be a fold in the body wall, known as a parapet, at this point, this parapet covers and protects the anemone when it is retracted; the oral disc has a central mouth slit-shaped, surrounded by one or more whorls of tentacles. The ends of the slit lead to grooves in the wall of the pharynx known as siphonoglyphs; the tentacles are tapered and tipped by a pore, but in some species they are branched, club-tipped, or reduced to low knobs. The tentacles are armed with many cnidocytes, cells that are both defensive and used to capture prey. Cnidocytes contain stinging nematocysts, capsule-like organelles capable of everting giving the phylum Cnidaria its name; each nematocyst contains a small venom vesicle filled with actinotoxins, an inner filament, an external sensory hair. A touch to the hair mechanically triggers a cell explosion, which launches a harpoon-like structure that attaches to the organism that triggered it, injects a dose of venom in the flesh of the aggressor or prey.
At the base of the tentacles in some species lie acrorhagi, elongated inflatable tentacle-like organs armed with cnidocytes, that can flail around and fend off other encroaching anemones. The venom is a mix of toxins, including neurotoxins, that paralyzes the prey so the anemone can move it to the mouth for digestion inside the gastrovascular cavity. Actinotoxins are toxic to prey species of fish and crustaceans. However, small banded fish in various colours, are not affected by their host anemone's sting and shelter themselves from predators among its tentacles. Several other species have similar adaptions and are unaffected. Most sea anemones are harmless to humans, but a few toxic species have caused severe injuries and are lethal. Sea anemones have. Waste and undigested matter is excreted through this opening; the mouth is slit-like in shape, bears a groove at one or both ends. The groove, termed a siphonoglyph, is ciliated, helps to move food particles inwards and circulate water through the gastrovascular cavity.
The mouth opens into a flattened pharynx. This consists of an in-folding of the body wall, is therefore lined by the animal's epidermis; the pharynx runs for about one third the length of the body before opening into the gastrovascular cavity that occupies the remainder of the body. The gastrovascular cavity itself is divided into a number of chambers by mesenteries radiating inwards from the body wall; some of the mesenteries form complete partitions with a free edge at the base of the pharynx, where t