Misplaced Pages

#254745

85-433: An introitus is an entrance into a canal or hollow organ . The vaginal introitus is the opening that leads to the vaginal canal. This anatomy article is a stub . You can help Misplaced Pages by expanding it . Organ (anatomy) An organ's tissues can be broadly categorized as parenchyma , the functional tissue, and stroma , the structural tissue with supportive, connective, or ancillary functions. For example,

170-404: A metachronal rhythm rather like that of a Mexican wave . From each balancer in the statocyst a ciliary groove runs out under the dome and then splits to connect with two adjacent comb rows, and in some species runs along the comb rows. This forms a mechanical system for transmitting the beat rhythm from the combs to the balancers, via water disturbances created by the cilia. The Lobata has

255-469: A phylum of marine invertebrates , commonly known as comb jellies , that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and they are the largest animals to swim with the help of cilia. Depending on the species, adult ctenophores range from a few millimeters to 1.5 m (5 ft) in size. Only 186 living species are currently recognised. Their bodies consist of

340-402: A "darting motion". Most Platyctenida have oval bodies that are flattened in the oral-aboral direction, with a pair of tentilla-bearing tentacles on the aboral surface. They cling to and creep on surfaces by everting the pharynx and using it as a muscular "foot". All but one of the known platyctenid species lack comb-rows. Platyctenids are usually cryptically colored, live on rocks, algae, or

425-571: A domed head with vesicles (chambers) that contain adhesive; a stalk that anchors the cell in the lower layer of the epidermis or in the mesoglea; and a spiral thread that coils round the stalk and is attached to the head and to the root of the stalk. The function of the spiral thread is uncertain, but it may absorb stress when prey tries to escape, and thus prevent the colloblast from being torn apart. One species, Minictena luteola, which only measure 1.5mm in diameter, have five different types of colloblast cells. In addition to colloblasts, members of

510-421: A few ctenophore species lack them. Like cnidarians, ctenophores have two main layers of cells that sandwich a middle layer of jelly-like material, which is called the mesoglea in cnidarians and ctenophores; more complex animals have three main cell layers and no intermediate jelly-like layer. Hence ctenophores and cnidarians have traditionally been labelled diploblastic . Both ctenophores and cnidarians have

595-462: A mass of jelly, with a layer two cells thick on the outside, and another lining the internal cavity. The phylum has a wide range of body forms, including the egg-shaped cydippids with a pair of retractable tentacles that capture prey, the flat, generally combless platyctenids , and the large-mouthed beroids , which prey on other ctenophores. Almost all ctenophores function as predators , taking prey ranging from microscopic larvae and rotifers to

680-400: A mouth that can usually be closed by muscles; a pharynx ("throat"); a wider area in the center that acts as a stomach ; and a system of internal canals. These branch through the mesoglea to the most active parts of the animal: the mouth and pharynx; the roots of the tentacles, if present; all along the underside of each comb row; and four branches around the sensory complex at the far end from

765-576: A nervous system, with the genes coding for the receptors for each of these neurotransmitters missing. Monofunctional catalase (CAT), one of the three major families of antioxidant enzymes that target hydrogen peroxide , an important signaling molecule for synaptic and neuronal activity, is also absent, most likely due to gene loss. They have been found to use L-glutamate as a neurotransmitter , and have an unusually high variety of ionotropic glutamate receptors and genes for glutamate synthesis and transport compared to other metazoans. The genomic content of

850-566: A pair of lobes, which are muscular, cuplike extensions of the body that project beyond the mouth. Their inconspicuous tentacles originate from the corners of the mouth, running in convoluted grooves and spreading out over the inner surface of the lobes (rather than trailing far behind, as in the Cydippida). Between the lobes on either side of the mouth, many species of lobates have four auricles, gelatinous projections edged with cilia that produce water currents that help direct microscopic prey toward

935-452: A relatively thick, jelly-like mesoglea sandwiched between two epithelia , layers of cells bound by inter-cell connections and by a fibrous basement membrane that they secrete . The epithelia of ctenophores have two layers of cells rather than one, and some of the cells in the upper layer have several cilia per cell. The outer layer of the epidermis (outer skin) consists of: sensory cells; cells that secrete mucus , which protects

SECTION 10

#1732791384255

1020-454: A ring around the mouth. The only known ctenophores with long nerves today is Euplokamis in the order Cydippida. Their nerve cells arise from the same progenitor cells as the colloblasts. In addition there is a less organized mesogleal nerve net consisting of single neurites. The largest single sensory feature is the aboral organ (at the opposite end from the mouth), which is underlined with its own nerve net. This organ's main component

1105-414: A supporting function. These normally beat so that the propulsion stroke is away from the mouth, although they can also reverse direction. Hence ctenophores usually swim in the direction in which the mouth is eating, unlike jellyfish . When trying to escape predators, one species can accelerate to six times its normal speed; some other species reverse direction as part of their escape behavior, by reversing

1190-499: A type of muscle that, in more complex animals, arises from the middle cell layer , and as a result some recent text books classify ctenophores as triploblastic , while others still regard them as diploblastic. The comb jellies have more than 80 different cell types , exceeding the numbers from other groups like placozoans, sponges, cnidarians, and some deep-branching bilaterians. Ranging from about 1 millimeter (0.04 in) to 1.5 meters (5 ft) in size, ctenophores are

1275-416: A variety of organ systems . These specific systems are widely studied in human anatomy . The functions of these organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via a shared organ, the hypothalamus . For this reason, the two systems are combined and studied as the neuroendocrine system . The same is true for the musculoskeletal system because of

1360-687: A whole, are referred to as the Organon because logic is a tool for philosophical thinking. Earlier thinkers, such as those who wrote texts in the Hippocratic corpus , generally did not believe that there were organs of the body but only different parts of the body. Some alchemists (e.g. Paracelsus ) adopted the Hermetic Qabalah assignment between the seven vital organs and the seven classical planets as follows: Chinese traditional medicine recognizes eleven organs, associated with

1445-400: Is a statocyst , a balance sensor consisting of a statolith, a tiny grain of calcium carbonate, supported on four bundles of cilia , called "balancers", that sense its orientation. The statocyst is protected by a transparent dome made of long, immobile cilia. A ctenophore does not automatically try to keep the statolith resting equally on all the balancers. Instead, its response is determined by

1530-404: Is circular rather than oval in cross-section, and the pharynx extends over the inner surfaces of the lobes. The Thalassocalycida , only discovered in 1978 and known from only one species, are medusa-like, with bodies that are shortened in the oral-aboral direction, and short comb-rows on the surface furthest from the mouth, originating from near the aboral pole. They capture prey by movements of

1615-405: Is not expected the populations will survive. The two limiting factors in saline lakes are availability of food and a varied diet, and high temperatures during hot summers. Because a parasitic isopod, Livoneca redmanii , was introduced at the same time, it is difficult to say how much of the ecological impact of invasive species is caused by the ctenophore alone. Ctenophores may be abundant during

1700-444: Is over they will not produce more gametes again until later. A population of Mertensia ovum in the central Baltic Sea have become paedogenetic , and consist solely of sexually mature larvae less than 1.6 mm. In Mnemiopsis leidyi , nitric oxide (NO) signaling is present both in adult tissues and differentially expressed in later embryonic stages suggesting the involvement of NO in developmental mechanisms. The mature form of

1785-660: Is partly parasitic . If food is plentiful, they can eat 10 times their own weight per day. While Beroe preys mainly on other ctenophores, other surface-water species prey on zooplankton (planktonic animals) ranging in size from the microscopic, including mollusc and fish larvae, to small adult crustaceans such as copepods , amphipods , and even krill . Members of the genus Haeckelia prey on jellyfish and incorporate their prey's nematocysts (stinging cells) into their own tentacles instead of colloblasts . Ctenophores have been compared to spiders in their wide range of techniques for capturing prey – some hang motionless in

SECTION 20

#1732791384255

1870-406: Is the placenta , which has evolved more than 100 times independently in vertebrates, has evolved relatively recently in some lineages, and exists in intermediate forms in extant taxa. Studies on the evolution of the placenta have identified a variety of genetic and physiological processes that contribute to the origin and evolution of organs, these include the re-purposing of existing animal tissues,

1955-403: The cydippid Pleurobrachia . Since the body of many species is almost radially symmetrical , the main axis is oral to aboral (from the mouth to the opposite end). However, since only two of the canals near the statocyst terminate in anal pores, ctenophores have no mirror-symmetry, although many have rotational symmetry. In other words, if the animal rotates in a half-circle it looks

2040-676: The five Chinese traditional elements and with yin and yang , as follows: The Chinese associated the five elements with the five planets (Jupiter, Mars, Venus, Saturn, and Mercury) similar to the way the classical planets were associated with different metals. The yin and yang distinction approximates the modern notion of solid and hollow organs. Ctenophora Ctenophora ( / t ə ˈ n ɒ f ər ə / tə- NOF -ər-ə ; sg. : ctenophore / ˈ t ɛ n ə f ɔːr , ˈ t iː n ə -/ TEN -ə-for, TEE -nə- ; from Ancient Greek κτείς (kteis)  'comb' and φέρω (pherō)  'to carry') comprise

2125-426: The gland 's tissue that makes the hormones is the parenchyma , whereas the stroma includes the nerves that innervate the parenchyma, the blood vessels that oxygenate and nourish it and carry away its metabolic wastes, and the connective tissues that provide a suitable place for it to be situated and anchored. The main tissues that make up an organ tend to have common embryologic origins, such as arising from

2210-418: The haruspices or the augurs in order to divine the future by their shape, dimensions or other factors. This practice remains an important ritual in some remote, tribal societies. The term "visceral" is contrasted with the term " parietal ", meaning "of or relating to the wall of a body part, organ or cavity " The two terms are often used in describing a membrane or piece of connective tissue, referring to

2295-417: The stomach , intestines , gallbladder , bladder , and rectum . In the thoracic cavity , the heart is a hollow, muscular organ. Splanchnology is the study of the viscera. The term "visceral" is contrasted with the term " parietal ", meaning "of or relating to the wall of a body part, organ or cavity ". The two terms are often used in describing a membrane or piece of connective tissue, referring to

2380-400: The striated muscle . The wriggling motion is produced by smooth muscles , but of a highly specialized type. Coiling around prey is accomplished largely by the return of the tentilla to their inactive state, but the coils may be tightened by smooth muscle. There are eight rows of combs that run from near the mouth to the opposite end, and are spaced evenly round the body. The "combs" beat in

2465-461: The 20th century, organ transplants began to take place as scientists knew more about the anatomy of organs. These came later in time as procedures were often dangerous and difficult. Both the source and method of obtaining the organ to transplant are major ethical issues to consider, and because organs as resources for transplant are always more limited than demand for them, various notions of justice, including distributive justice , are developed in

2550-701: The Greek suffix -φορος meaning "carrying". For a phylum with relatively few species, ctenophores have a wide range of body plans. Coastal species need to be tough enough to withstand waves and swirling sediment particles, while some oceanic species are so fragile that it is very difficult to capture them intact for study. In addition, oceanic species do not preserve well, and are known mainly from photographs and from observers' notes. Hence most attention has until recently concentrated on three coastal genera – Pleurobrachia , Beroe and Mnemiopsis . At least two textbooks base their descriptions of ctenophores on

2635-441: The acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types. The study of plant organs is covered in plant morphology . Organs of plants can be divided into vegetative and reproductive. Vegetative plant organs include roots , stems , and leaves . The reproductive organs are variable. In flowering plants , they are represented by the flower , seed and fruit . In conifers ,

Introitus - Misplaced Pages Continue

2720-559: The adults of small crustaceans ; the exceptions are juveniles of two species, which live as parasites on the salps on which adults of their species feed. Despite their soft, gelatinous bodies, fossils thought to represent ctenophores appear in Lagerstätten dating as far back as the early Cambrian , about 525 million years ago. The position of the ctenophores in the "tree of life" has long been debated in molecular phylogenetics studies. Biologists proposed that ctenophores constitute

2805-676: The adults, lack both tentacles and tentacle sheaths. In some groups, such as the flat, bottom-dwelling platyctenids, the juveniles behave more like true larvae. They live among the plankton and thus occupy a different ecological niche from their parents, only attaining the adult form by a more radical ontogeny after dropping to the sea-floor. At least in some species, juvenile ctenophores appear capable of producing small quantities of eggs and sperm while they are well below adult size, and adults produce eggs and sperm for as long as they have sufficient food. If they run short of food, they first stop producing eggs and sperm, and then shrink in size. When

2890-431: The animal's buoyancy by pumping water into or out of the mesoglea. The outer surface bears usually eight comb rows, called swimming-plates, which are used for swimming. The rows are oriented to run from near the mouth (the "oral pole") to the opposite end (the "aboral pole"), and are spaced more or less evenly around the body, although spacing patterns vary by species and in most species the comb rows extend only part of

2975-415: The animal's "mood", in other words, the overall state of the nervous system. For example, if a ctenophore with trailing tentacles captures prey, it will often put some comb rows into reverse, spinning the mouth towards the prey. Research supports the hypothesis that the ciliated larvae in cnidarians and bilaterians share an ancient and common origin. The larvae's apical organ is involved in the formation of

3060-472: The animals. Among animal phyla, the Ctenophores are more complex than sponges , about as complex as cnidarians ( jellyfish , sea anemones , etc.), and less complex than bilaterians (which include almost all other animals). Unlike sponges, both ctenophores and cnidarians have: Ctenophores are distinguished from all other animals by having colloblasts , which are sticky and adhere to prey, although

3145-415: The beating of their comb-rows. There are two known species, with worldwide distribution in warm, and warm-temperate waters: Cestum veneris (" Venus ' girdle") is among the largest ctenophores – up to 1.5 meters (4.9 ft) long, and can undulate slowly or quite rapidly. Velamen parallelum , which is typically less than 20 centimeters (0.66 ft) long, can move much faster in what has been described as

3230-443: The bell and possibly by using two short tentacles. The Cestida ("belt animals") are ribbon-shaped planktonic animals, with the mouth and aboral organ aligned in the middle of opposite edges of the ribbon. There is a pair of comb-rows along each aboral edge, and tentilla emerging from a groove all along the oral edge, which stream back across most of the wing-like body surface. Cestids can swim by undulating their bodies as well as by

3315-597: The body surfaces of other invertebrates, and are often revealed by their long tentacles with many side branches, seen streaming off the back of the ctenophore into the current. Adults of most species can regenerate tissues that are damaged or removed, although only platyctenids reproduce by cloning , splitting off from the edges of their flat bodies fragments that develop into new individuals. Lab research on Mnemiopsis leidyi also show that when two individuals have parts of their bodies removed, they are able to fuse together, including their nervous and digestive systems, even when

3400-412: The body; and interstitial cells, which can transform into other types of cell. In specialized parts of the body, the outer layer also contains colloblasts , found along the surface of tentacles and used in capturing prey, or cells bearing multiple large cilia, for locomotion. The inner layer of the epidermis contains a nerve net , and myoepithelial cells that act as muscles . The internal cavity forms:

3485-441: The cilia on their comb rows for propulsion, although Leucothea has long and active auricles whose movements also contribute to propulsion. Members of the lobate genera Bathocyroe and Ocyropsis can escape from danger by clapping their lobes, so that the jet of expelled water drives them back very quickly. Unlike cydippids, the movements of lobates' combs are coordinated by nerves rather than by water disturbances created by

Introitus - Misplaced Pages Continue

3570-452: The cilia, yet combs on the same row beat in the same Mexican wave style as the mechanically coordinated comb rows of cydippids and beroids. This may have enabled lobates to grow larger than cydippids and to have less egg-like shapes. An unusual species first described in 2000, Lobatolampea tetragona , has been classified as a lobate, although the lobes are "primitive" and the body is medusa -like when floating and disk-like when resting on

3655-409: The common coastal "sea gooseberry", Pleurobrachia , sometimes has an egg-shaped body with the mouth at the narrow end, although some individuals are more uniformly round. From opposite sides of the body extends a pair of long, slender tentacles, each housed in a sheath into which it can be withdrawn. Some species of cydippids have bodies that are flattened to various extents so that they are wider in

3740-479: The cydippid genus Pleurobrachia , are incapable of bioluminescence. When some species, including Bathyctena chuni , Euplokamis stationis and Eurhamphaea vexilligera , are disturbed, they produce secretions (ink) that luminesce at much the same wavelengths as their bodies. Juveniles will luminesce more brightly in relation to their body size than adults, whose luminescence is diffused over their bodies. Detailed statistical investigation has not suggested

3825-458: The deep-sea genus Bathocyroe is red, which hides the bioluminescence of copepods it has swallowed. The comb rows of most planktonic ctenophores produce a rainbow effect, which is not caused by bioluminescence but by the scattering of light as the combs move. Most species are also bioluminescent, but the light is usually blue or green and can only be seen in darkness. However some significant groups, including all known platyctenids and

3910-418: The distance from the aboral pole towards the mouth. The "combs" (also called "ctenes" or "comb plates") run across each row, and each consists of thousands of unusually long cilia, up to 2 millimeters (0.08 in). Unlike conventional cilia and flagella, which has a filament structure arranged in a 9 + 2 pattern, these cilia are arranged in a 9 + 3 pattern, where the extra compact filament is suspected to have

3995-451: The eight comb rows. In the genome of Mnemiopsis leidyi ten genes encode photoproteins. These genes are co-expressed with opsin genes in the developing photocytes of Mnemiopsis leidyi , raising the possibility that light production and light detection may be working together in these animals. Ctenophores are found in most marine environments: from polar waters at −2 °C to the tropics at 30 °C; near coasts and in mid-ocean; from

4080-402: The ethical analysis. This situation continues as long as transplantation relies upon organ donors rather than technological innovation, testing, and industrial manufacturing. The English word "organ" dates back to the twelfth century and refers to any musical instrument. By the late 14th century, the musical term's meaning had narrowed to refer specifically to the keyboard-based instrument . At

4165-504: The food supply improves, they grow back to normal size and then resume reproduction. These features make ctenophores capable of increasing their populations very quickly. Members of the Lobata and Cydippida also have a reproduction form called dissogeny; two sexually mature stages, first as larva and later as juveniles and adults. During their time as larva they are capable of releasing gametes periodically. After their first reproductive period

4250-420: The function of ctenophores' bioluminescence nor produced any correlation between its exact color and any aspect of the animals' environments, such as depth or whether they live in coastal or mid-ocean waters. In ctenophores, bioluminescence is caused by the activation of calcium-activated proteins named photoproteins in cells called photocytes , which are often confined to the meridional canals that underlie

4335-447: The genus Haeckelia , which feed mainly on jellyfish , incorporate their victims' stinging nematocytes into their own tentacles – some cnidaria-eating nudibranchs similarly incorporate nematocytes into their bodies for defense. The tentilla of Euplokamis differ significantly from those of other cydippids: they contain striated muscle , a cell type otherwise unknown in the phylum Ctenophora; and they are coiled when relaxed, while

SECTION 50

#1732791384255

4420-424: The genus Mnemiopsis , and it is thought that most of the hermaphroditic species are self-fertile. Development of the fertilized eggs is direct; there is no distinctive larval form. Juveniles of all groups are generally planktonic , and most species resemble miniature adult cydippids, gradually developing their adult body forms as they grow. In the genus Beroe , however, the juveniles have large mouths and, like

4505-420: The genus Ocyropsis and Bathocyroe fosteri in the genus Bathocyroe . The gonads are located in the parts of the internal canal network under the comb rows, and eggs and sperm are released via pores in the epidermis. Fertilization is generally external , but platyctenids use internal fertilization and keep the eggs in brood chambers until they hatch. Self-fertilization has occasionally been seen in species of

4590-486: The largest non-colonial animals that use cilia as their main method of locomotion. Most species have eight strips, called comb rows, that run the length of their bodies and bear comb-like bands of cilia, called "ctenes", stacked along the comb rows so that when the cilia beat, those of each comb touch the comb below. The name "ctenophora" means "comb-bearing", from the Greek κτείς (stem-form κτεν- ) meaning "comb" and

4675-468: The liver and heart evolved in the chordates about 550-500 million years ago, while the gut and brain are even more ancient, arising in the ancestor of vertebrates, insects, molluscs, and worms about 700–650 million years ago. Given the ancient origin of most vertebrate organs, researchers have looked for model systems, where organs have evolved more recently, and ideally have evolved multiple times independently. An outstanding model for this kind of research

4760-416: The mouth "lips" in some species of Beroe , is a pair of narrow strips of adhesive epithelial cells on the stomach wall that "zip" the mouth shut when the animal is not feeding, by forming intercellular connections with the opposite adhesive strip. This tight closure streamlines the front of the animal when it is pursuing prey. The Ganeshida has a pair of small oral lobes and a pair of tentacles. The body

4845-577: The mouth – two of these four branches terminate in anal pores. The inner surface of the cavity is lined with an epithelium , the gastrodermis . The mouth and pharynx have both cilia and well-developed muscles. In other parts of the canal system, the gastrodermis is different on the sides nearest to and furthest from the organ that it supplies. The nearer side is composed of tall nutritive cells that store nutrients in vacuoles (internal compartments), germ cells that produce eggs or sperm, and photocytes that produce bioluminescence . The side furthest from

4930-411: The mouth. This combination of structures enables lobates to feed continuously on suspended planktonic prey. Lobates have eight comb-rows, originating at the aboral pole and usually not extending beyond the body to the lobes; in species with (four) auricles, the cilia edging the auricles are extensions of cilia in four of the comb rows. Most lobates are quite passive when moving through the water, using

5015-678: The nervous system genes is the smallest known of any animal, and could represent the minimum genetic requirements for a functional nervous system. The fact that portions of the nervous system feature directly fused neurons, without synapses, suggests that ctenophores might form a sister group to other metazoans, having developed a nervous system independently. If ctenophores are the sister group to all other metazoans, nervous systems may have either been lost in sponges and placozoans, or arisen more than once among metazoans. Cydippid ctenophores have bodies that are more or less rounded, sometimes nearly spherical and other times more cylindrical or egg-shaped;

5100-518: The nervous system. The aboral organ of comb jellies is not homologous with the apical organ in other animals, and the formation of their nervous system has therefore a different embryonic origin. Ctenophore nerve cells and nervous system have different biochemistry as compared to other animals. For instance, they lack the genes and enzymes required to manufacture neurotransmitters like serotonin , dopamine , nitric oxide , octopamine , noradrenaline , and others, otherwise seen in all other animals with

5185-420: The neurons are found to have synaptic connections , but the neurons in the nerve net are highly distinctive by being fused into a syncytium , rather than being connected by synapses. Some animals outside ctenophores also have fused nerve cells, but never to such a degree that they form a whole nerve net. Fossils shows that Cambrian species had a more complex nervous system, with long nerves which connected with

SECTION 60

#1732791384255

5270-467: The new generation of plants (see clonal colony ). Many societies have a system for organ donation , in which a living or deceased donor's organ are transplanted into a person with a failing organ. The transplantation of larger solid organs often requires immunosuppression to prevent organ rejection or graft-versus-host disease . There is considerable interest throughout the world in creating laboratory-grown or artificial organs . Beginning in

5355-430: The nutritive cells. The ciliary rosettes in the canals may help to transport nutrients to muscles in the mesoglea. The anal pores may eject unwanted small particles, but most unwanted matter is regurgitated via the mouth. Little is known about how ctenophores get rid of waste products produced by the cells. The ciliary rosettes in the gastrodermis may help to remove wastes from the mesoglea, and may also help to adjust

5440-403: The opposing sides. Aristotle used the word frequently in his philosophy, both to describe the organs of plants or animals (e.g. the roots of a tree, the heart or liver of an animal) because, in ancient Greek, the word ' organon ' means 'tool', and Aristotle believed that the organs of the body were tools for us by means of which we can do things. For similar reasons, his logical works, taken as

5525-406: The opposing sides. The organ level of organisation in animals can be first detected in flatworms and the more derived phyla , i.e. the bilaterians . The less-advanced taxa (i.e. Placozoa , Porifera , Ctenophora and Cnidaria ) do not show consolidation of their tissues into organs. More complex animals are composed of different organs, which have evolved over time. For example,

5610-415: The organ is covered with ciliated cells that circulate water through the canals, punctuated by ciliary rosettes, pores that are surrounded by double whorls of cilia and connect to the mesoglea. When prey is swallowed, it is liquefied in the pharynx by enzymes and by muscular contractions of the pharynx. The resulting slurry is wafted through the canal system by the beating of the cilia , and digested by

5695-514: The organ that bears the reproductive structures is called a cone . In other divisions ( phyla ) of plants, the reproductive organs are called strobili , in Lycopodiophyta , or simply gametophores in mosses . Common organ system designations in plants include the differentiation of shoot and root. All parts of the plant above ground (in non- epiphytes ), including the functionally distinct leaf and flower organs, may be classified together as

5780-435: The plane of the tentacles. The tentacles of cydippid ctenophores are typically fringed with tentilla ("little tentacles"), although a few genera have simple tentacles without these side branches. The tentacles and tentilla are densely covered with microscopic colloblasts that capture prey by sticking to it. Colloblasts are specialized mushroom -shaped cells in the outer layer of the epidermis, and have three main components:

5865-526: The power stroke of the comb plate cilia. It is uncertain how ctenophores control their buoyancy, but experiments have shown that some species rely on osmotic pressure to adapt to the water of different densities. Their body fluids are normally as concentrated as seawater. If they enter less dense brackish water, the ciliary rosettes in the body cavity may pump this into the mesoglea to increase its bulk and decrease its density, to avoid sinking. Conversely, if they move from brackish to full-strength seawater,

5950-514: The presence of specific ctenophore genes that were markedly different from those of other species. Follow up analysis by Whelan et al. (2017) yielded further support for the 'Ctenophora sister' hypothesis; the issue remains a matter of taxonomic dispute. Schultz et al. (2023) found irreversible changes in synteny in the sister of the Ctenophora, the Myriazoa , consisting of the rest of

6035-413: The relationship between the muscular and skeletal systems . In the study of anatomy , viscera ( sg. : viscus ) refers to the internal organs of the abdominal , thoracic , and pelvic cavities . The abdominal organs may be classified as solid organs or hollow organs . The solid organs are the liver , pancreas , spleen , kidneys , and adrenal glands . The hollow organs of the abdomen are

6120-472: The rosettes may pump water out of the mesoglea to reduce its volume and increase its density. Ctenophores have no brain or central nervous system , but instead have a subepidermal nerve net (rather like a cobweb) that forms a ring round the mouth and is densest near structures such as the comb rows, pharynx, tentacles (if present) and the sensory complex furthest from the mouth. The communication between nerve cells make use of two different methods; some of

6205-534: The same germ layer . Organs exist in most multicellular organisms . In single-celled organisms such as members of the eukaryotes , the functional analogue of an organ is known as an organelle . In plants, there are three main organs. The number of organs in any organism depends on the definition used. There are approxiamately 79 Organs in the human body,but it is something that is debated as not all scientist agree on what counts as an organ. Except for placozoans , multicellular animals including humans have

6290-447: The same as when it started. The Ctenophore phylum has a wide range of body forms, including the flattened, deep-sea platyctenids , in which the adults of most species lack combs, and the coastal beroids , which lack tentacles and prey on other ctenophores by using huge mouths armed with groups of large, stiffened cilia that act as teeth. Like those of cnidarians , ( jellyfish , sea anemones , etc.), ctenophores' bodies consist of

6375-513: The same species is also able to revert back to the cydippid stage when triggered by environmental stressors. Most ctenophores that live near the surface are mostly colorless and almost transparent. However some deeper-living species are strongly pigmented, for example the species known as "Tortugas red" (see illustration here), which has not yet been formally described. Platyctenids generally live attached to other sea-bottom organisms, and often have similar colors to these host organisms. The gut of

6460-489: The same time, a second meaning arose, in reference to a "body part adapted to a certain function". Plant organs are made from tissue composed of different types of tissue. The three tissue types are ground, vascular, and dermal. When three or more organs are present, it is called an organ system. The adjective visceral , also splanchnic , is used for anything pertaining to the internal organs. Historically, viscera of animals were examined by Roman pagan priests like

6545-411: The sea-bed. The Beroida , also known as Nuda , have no feeding appendages, but their large pharynx , just inside the large mouth and filling most of the saclike body, bears "macrocilia" at the oral end. These fused bundles of several thousand large cilia are able to "bite" off pieces of prey that are too large to swallow whole – almost always other ctenophores. In front of the field of macrocilia, on

6630-453: The second-earliest branching animal lineage, with sponges being the sister-group to all other multicellular animals ( Porifera sister hypothesis ). Other biologists contend that ctenophores emerged earlier than sponges ( Ctenophora sister hypothesis ), which themselves appeared before the split between cnidarians and bilaterians . Pisani et al . reanalyzed the data and suggested that the computer algorithms used for analysis were misled by

6715-409: The shoot organ system. The vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as photosynthesis , while the reproductive organs are essential in reproduction . However, if there is asexual vegetative reproduction , the vegetative organs are those that create

6800-473: The summer months in some coastal locations, but in other places, they are uncommon and difficult to find. In bays where they occur in very high numbers, predation by ctenophores may control the populations of small zooplanktonic organisms such as copepods , which might otherwise wipe out the phytoplankton (planktonic plants), which are a vital part of marine food chains . Almost all ctenophores are predators – there are no vegetarians and only one genus that

6885-503: The surface waters to the ocean depths at more than 7000 meters. The best-understood are the genera Pleurobrachia , Beroe and Mnemiopsis , as these planktonic coastal forms are among the most likely to be collected near shore. No ctenophores have been found in fresh water. In 2013 Mnemiopsis was recorded in lake Birket Qarun, and in 2014 in lake El Rayan II, both near Faiyum in Egypt, where they were accidentally introduced by

6970-400: The tentilla of all other known ctenophores elongate when relaxed. Euplokamis ' tentilla have three types of movement that are used in capturing prey: they may flick out very quickly (in 40 to 60  milliseconds ); they can wriggle, which may lure prey by behaving like small planktonic worms; and they coil round prey. The unique flicking is an uncoiling movement powered by contraction of

7055-399: The transport of fish (mullet) fry. Though many species prefer brackish waters like estuaries and coastal lagoons in open connection with the sea, this was the first record from an inland environment. Both lakes are saline, with Birket Qarun being hypersaline, and shows that some ctenophores can establish themselves in saline limnic environments without connection to the ocean. In the long run it

7140-537: The two individuals are genetically different; a phenomenon that has so far only been found in comb jellies. The last common ancestor (LCA) of the ctenophores was hermaphroditic . Some are simultaneous hermaphrodites, which can produce both eggs and sperm at the same time, while others are sequential hermaphrodites, in which the eggs and sperm mature at different times. There is no metamorphosis . At least three species are known to have evolved separate sexes ( dioecy ); Ocyropsis crystallina and Ocyropsis maculata in

7225-542: The water using their tentacles as "webs", some are ambush predators like Salticid jumping spiders , and some dangle a sticky droplet at the end of a fine thread, as bolas spiders do. This variety explains the wide range of body forms in a phylum with rather few species. The two-tentacled "cydippid" Lampea feeds exclusively on salps , close relatives of sea-squirts that form large chain-like floating colonies, and juveniles of Lampea attach themselves like parasites to salps that are too large for them to swallow. Members of

#254745