Causes of Polymorphism 3. It is situated at the apex of the colony. The sessile polyp form has, in fact, two types of polyps. Soon, a cavity called enteron develops in the solid endodermal cell mass by the process of delamination and the planula becomes a two-layered larva having an outer ciliated ectodermal cells and an inner layer of endodermal cells. They are mainly two types. Each kind of zooid is specialized to perform a … Obelia belongs to which class of phylum coelenterata . 3. Advancement of Medusa over Polyp: Medusa exhibits many features of advancement over polyp, few of them are as follows: 1. Medusa swims freely on the surface water. It is with the lower ring that the statocysts are connected. Polymorphism occurs in. and the free swimming medusae are reproductive nature. The polyp performs vegetative function such as feeding, respiration, etc. Polymorphism : Coelenterates having more than three types of individuals are called polymorphic, e.g. Both of them are formed on the same pattern. cells attached that capture food. Suppose the tentacular region of a polyp to be pulled out, as it were, into a disc-like form and afterwards to be bent into the form of saucer with the concavity distal, that is towards the manubrium. It contains gas chambers inside. The word polymorphism means having many forms. 97. Chitinous covering ocer the colony of Obelia is: A. Coenosarc: B. Perisarc: C. Cuticle: D. None of these View Answer Workspace Report Discuss in Forum. A detailed analysis is made of stolonic growth typical of both free and attached stolons. The presence of the four radial canals distinguishes the four principal radii or per-radii. The cnidoblasts are found in the basal part of the hydranth and in the coenosarc. Thus, an asexual polypoid generation alternates with a sexual medusoid generation. C++ polymorphism means that a call to a member function will cause a different function to be executed depending on the type of object that invokes the function. A polymorphic colony contains many individuals called zooids. ADVERTISEMENTS: In this article we will discuss about Polymorphism in Cnidarians:- 1. The medusa is circular and tiny umbrella-like in shape. Around the gastrozooid a number of gonozooids are present Gastrozooid is a modified polyp. This is a special character of coelenterata occurring only in them (a) Flame cells (b) Hermaphroditism (c) Nematocysts (d) Polymorphism. The blastostyle has no mouth and no tentacles, but ends distally into a flattened disc. Towards the base of the hydrocaulus in the axils of the polyps, are reproductive polyps called blastostyles. In Physalia the gonozooid shows branched stalk, bearing clusters of gonophores (gonopalpon). The members of the colony develop from coenosarc. It is represented by polyp form. Dimorphism: Many hydrozoan colonies like Tubularia and Campanularia have only two types of zooids, the feeding zooids or gastrozooids and medusae or nectophores that bud off from the stem or gastrozooids. Projecting from the middle of the radial canals are four gonads, since sexes are separate they are either four testes or four ovaries,they are patches of modified sub-umbrellar ectoderm. According to this theory the polymorphic individual is a single organism. From the enteric cavity, arise four radial canals which are delicate ciliated tubes, they run to the margin of the bell to join a ciliated circular canal running near the margin. The two types of zooids are, Gastrozooids are concerned with feeding. The endoderm cells have no muscle processes, they are ciliated epithelial cells, they are digestive. The nematocysts are abundant on the tentacles and manubrium only. Obelia shows polymorphism in which the polyps are for feeding the colony, blastostyles for budding and medusae for disseminating gametes. 5. It is filled with air. Before sharing your knowledge on this site, please read the following pages: 1. The medusae are modified zooids capable of free swimming existence and moreover they are not produced directly from a zygote but are budded off from the blastostyle. Occurance in the same species of more than one type of individuals, which differ in form and function, is known as polymorphism. This is a special mode of asexual reproduction. 32.3) is club-shaped, cylindrical form. Some cells migrate into blastocoele, eventually filling it completely to form a solid gastrula known as stereo gastrula. D. Hydrozoa. Definition of Polymorphism: Polymorphism may be defined as the “phenomenon of existence of different physiological and morphological forms represented by an extensive range of variation within a … Answer: (c) 7. The growth cycle of O. commissularis McCrady is analysed in terms of tissue mass and shape, cell number and cell transformations. It may be defined in another way, polymorphism means “the existence of individuals (zooids) of a single species in more than one forms and functions.” Anthozoa. The polymorphic tendency reached its peak in coelenterate organisms belonging to order 'Siphanophora' of class 'Hydrozoa'. Indeed, the use of the FD-type phylum profile to distinguish the FD from the HC was revealed to have such high sensitivity and specificity in the present study that they were found to be especially effective for identifying a subtype of FD that is associated … The polyp represents the asexual phase which is a prominent branched hydroid colony found attached to rocks, stones, shells of animals, wooden pilings etc. One individual possesses the power to reproduce the other by asexual reproduction, which again by sexual reproduction gives rise to the next generation. In it not only cells are specialized but individuals get specialized to perform different functions. Answer: (c) 5. You can overload a method with different sets of parameters. The body and manubrium of the polyp enclose a spacious enteric cavity or gastro vascular cavity. 3.Gonozooids : It is a reproductive zooid. The ocelli consist of patches of pigment and photoreceptor cells organised either within a flat disc or a pit. The endoderm of tentacles has cubical, vacuolated cells with thick walls. In coelenterates the different individuals or zooids often get united in the form of a colony. Many such cormidia are arranged on the coenosarcal stalk. Origin 5. Polymorphism the feature of the population which includes more than one type of structurally and functionally different individuals. it is cup- like in … Hydrozoa belongs to the phylum Cnidaria, which are aquatic (mainly marine) organisms that are relatively simple in structure.. Obelia is also called sea fur. The mode of sexual reproduction provides wide dispersal of the species due to its free swimming habit. The epidermis resembles the epithelium of higher Metazoa forming a thin, protective and sensitive layer of small cells. The two layers of ectoderm which enclose the bell rudiment from outside now break leaving a marginal and circular shelf called velum. Digestive enzymes are secreted from the endoderm of bulbs. In this way a medusa is derived completely from a polyp (Fig. 2) Blastostyle (asexually, reproducing zooid). According to them the indivldualsof the colony are the organs of a single medusoid individual i.e., mouth, tentacles, manubrium of the zooid will multiply into different types of zooids and migrate from their original position. These forms or zooids are developed from polyps or medusae. Their basal tentacle is un branched. Obelia like animals Show two forms, polyp nutritive zooid and medusa reproductive zooid. From such a form the actual condition of things found in the medusa would be produced by the continuous cavity in the bell being for most part obliterated by the growing together of its walls so as to form the endodermal lamella. It is one of the most dreaded and most beautiful pelagic coelenterate found floating in tropical and subtropical oceans. The cavity of the bell rudiment assumes the shape of the sub-umbrella, and a manubrium is formed in the centre. Occurance in the same species of more than one type of individuals, which differ in form and function, is known as polymorphism. The germ cells of Obelia do not arise in the gonads, they arise from interstitial cells of the ectoderm of the blastostyle where they may be seen in various stages of maturation, then they migrate into the medusa, then through the radial canals they take up their position in the ectoderm of the gonads. Where organism attaches. At its base a long tentacle is present. Exhibits by many Hydrozoan colonies; Examples: Obelia , Tubularia; 2. The enteron has a fluid and its lining is flagellated. Each cormodium includes. Therefore, a true alternation of generations is always between a diploid asexual and haploid sexual generations, as is exhibited by fern plant. The hydrorhiza and hydrocaulus are hollow tubes. Pulsation will continue in the bell as long as any portion of the ring is intact. Gene polymorphisms can occur in any region of the genome. It has mouth at its apex. 2.Nectocalyces : These are swimming-bells. They are helpful in the capturing the prey. Examples of polymorphic colonies are Obelia, Physalia , Porpita, etc. The medusae are sexual or reproductive zooids possessing gonads. Hence the term metagenesis is used to replace the term alternation of generations in Obelia. A gonad has an outer ectoderm and inner endoderm with mesogloea between the two layers. They are muscular. The characteristic larva in coelenterates is (a) Oncosphere (b) Rhabditiform (c) Planula (d) Cysticercus. The life history may be represented as male and female gametes → zygote → planula larva → hydrula → colony → sexual medusae → gametes → zygote and so on. Which of these exhibits phenomenon of polymorphism: A. Physaila: B. Obelia: C. Both (a) & (b) D. None of these View Answer ... View Answer Workspace Report Discuss in Forum. The muscular system of medusa is somewhat more specialised than in the polyp. The lower ring is the centre of rhythmic pulsations, i.e., it contains the pacemakers. The majority of polymorphisms are silent, meaning they do not alter the function or expression of a gene. biology. Rhythmical contractions of the hydranths cause a current which distributes food obtained by some polyps to those parts of the colony where feeding is not taking place. The result of this to be a medusa-like body with a double wall to the entire bell, the narrow space between the two layers containing a prolongation of coelenteron and being lined with gastro dermis. TOS4. It is covered by a transparent gonotheca and contains an axis or blastostyle on which lateral buds form that develop into medusae or gonophores. Inside the cnidoblast an oval or pyriform bladder called as stinging capsule is present. 2. They resemble the gastrozooids. The hydrotheca has a shelf across the base which supports the hydranth, and the hydranth can contract and withdraw into the hydrotheca. The Obelia is a trimorphic colony, that is, having three kinds of zooids which are as follows: 1. Trimorphism: Some species like Obelia and Plumularia are trimorphic because besides gastrozooids and medusa, they also have medusa-producing gonozooids or blastostyle. The tentacles are longer than hypostome, tapering and filiform. 7. Polymorphism is associated with life history of a coelenterate animal. Obelia is cosmopolitan in distribution, forming a whitish or light-brown plant-like fur in the sea; hence, the common name sea-fur is assigned to it. The Hydroids; Polymorphism (Majority time in Polyp stage) Genus Hydra, Tentacles. It shows mouth and tentacles at the free end. Each colony of Obelia consists of a horizontal thread-like root called hydrorhiza which is attached to a weed or any substratum. It has a mouth at its tip. A) Hydrozoa done clear. According to them siphonophores are polymorphic colonies of modified polyps which can produce medusae. The distal ectoderm of the vesicle separates into two layers, then the inner layer of ectoderm splits to acquire a cavity called a bell rudiment. Trimorphism: Some species like Obelia and Plumularia are trimorphic because besides gastrozooids and medusa, they also have medusa-producing gonozooids or blastostyle. Near the base of a gastrozooid usually a single, long and contractile tentacle arises. 3) Medusae are present. It is a characteristic feature of Cnidarians, particularly the polyp and medusa forms, or of zooids within colonial organisms like … (B) Physalia: Physalia is a polymorphic colony of bright blue colour belonging to suborder Physophorida of the order Siphonophora. Medusa in Oral View Patterns of polymorphism: Degree of polymorphism varies greatly in different groups of Hydrozoa. In Physalia, the tentacle is very long. Dactylozooid : It is a modified polyp. On lower side of the float a big gastrozooid is present. Some polymorphism is visible. The gastro dermal cells lack contractile extensions, and the muscular system is, thus, restricted to the epidermal layer. Such a colony is called polymorphic and the phenomenon is known as polymorphism. I. Halistemma: This Siphonophora organism will show the greatestpolymorphic tendency. For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free-living or sexually reproducing individuals, the medusae. On this, groups of zooids will be present called cormidia. When the reproductive buds mature, they break off and become free-swimming medusa, which are either … This website includes study notes, research papers, essays, articles and other allied information submitted by visitors like YOU. Java supports two kinds of polymorphism. Medusa exhibits many features of advancement over polyp, few of them are as follows: 1. Many siphonophora organisms will show complicated structures. Cnidoblast is an oval or rounded cell with a basal nucleus on one side. Nutritive polyp. Gonozooid : They produce medusae which take up sexual reproduction. However, the parent medusae die soon after liberating their respective gametes. These are called polymorphism. Horizontal movement is dependent upon water currents. It performs all functions. Polymorphism occurs in. In coelenterates the different individuals or zooids often get united in the form of a colony. well represented by polymorphic hydrozoan like Obelia. The gonad has a small diverticulum of the radial canal. its outer layer of ectoderm cells becomes ciliated, and now it is called planula. It is abundant in both Atlantic and Pacific coastal waters. The food consists of living animals or bodies of animals. In velella and Porpita the margin of the colony bears long and hollow tentacles. 3. The different individuals are called zooids. 1) polymorphism is found in puccinia/Aspergillus/Peziza. b) Siphonosome : The coenosaroal stalk below the swimming bells is siphanosome. Polymorphism is found in . Obelia is sedentary, marine colonial form found attached on the surface of sea weeds, molluscan shells, rocks and wooden piles in shallow water up to 80 metres in depth. They are tubular. 3. 2. Gonotheca, blastostyle and the gonophores together form a gonangium. C. Rhizopoda. The term metagenesis is used for such alternation of fixed and free phases. Polyps or hydranths (nutritive zooids); 2. The tentacle shows branches called Tentilla'. It is represented by polyp form. Genus Hydra, Basal Disc. Polymorphism. 1)The pneumatophore is small in Halistemma. Alternation of Generations and Metagenesis of Obelia: The best answers are voted up and rise to the top. When the temperature of the water exceeds 20°C, the buds which would normally form gonangia in the colony break free from the colony and settle down; a stolon arises from the lower end of the bud which produces a new colony of Obelia asexually. These zooids are protective in function. Each of these classes can provide its own implementation of the interface. Obelia like animals Show two forms, polyp nutritive zooid and medusa reproductive zooid. Polymorphism – A Characteristic Feature of Coelenterates (Cnidaria) The occurrence of structurally and functionally more than two different types of individuals, called the zooids within the same organism is called polymorphism. Each individual member of Coelenterates is known as Zooid and they often units to form a colony which acts as a single unit (individual). Because, in Obelia, there are no true two generations to alternate each other. It performs all functions. It consists of branched filaments approximately the thickness of fine sewing cotton. Alteration of generations. This bulb is filled with poisonous fluid or hypnotoxin, which is chemically a mixture of proteins and phenols. Fig. Which part of the male reproductive system store the sperm? The blastostyle also produces medusae by asexual budding. Branches emerging from the stem terminate either in nutritive zooids, called the polyps or hydranths or in reproductive zooids called blastostyles or gonangia , which produce medusa. The outer, exumbrellar surface of the medusa is homologous with the base of the polyp providing attachment with the parental colony. The free distal end is produced into a conical elevation, the hypostome or manubrium which is about one-third of the length of the hydranth. Anus is absent in both the cases. Gonozooids : The reproductive zooids are called gonozooids. Disclaimer Copyright, Share Your Knowledge Zoology, Invertebrate Zoology, Phylum Coelenterata, Colonial Hydrozoans, Obelia. On this tentacle many nematocysts are present. The enormous development of mesogloea reduces the gastro vascular cavity or enteron to a system of canals and also provides lightness which helps in buoyancy. It is saucer-shaped, it is attached by the middle of the convex surface to the blastostyle, when fully formed it breaks free and emerges from the mouth of the gonotheca. Velum is characteristic of hydrozoan medusae but it is insignificant in Obelia. The gonangium (Gr., gonos = seed; angeion = vessel) (Fig. On each side of the mesogloea is a nerve net composed of nerve cells and their fibres, the two nerve nets are inter-connected. The perisarc around a blastostyle is a gonotheca, the blastostyle and gonotheca are together called a gonangium. Email This BlogThis! Share Your PDF File 7. The most primitive invertebrate to possess musculo- epithelial cells and nerve cells is PowerPoint … It is useful to float the cobny on the water. Dactylo zooids : They are called Palpons, feelers or tasters. They are called' Feelers' or Palpons. There are eight marginal sense organs called statocysts or lithocysts lying at regular intervals, being attached on the sub-umbrella side to the bulbs of eight tentacles, they are developed in response to a locomotory habit. Trimorphism: Some species like Obelia and Plumularia are trimorphic because besides gastrozooids and medusa, they also have medusa-producing gonozooids or blastostyle. This phenomenon is known as alternation of generations, till recently. Thus porpita shows polymorphic tendency. 4. Obelia like animals Show two forms, polyp nutritive zooid and medusa reproductive zooid. They have no mouth. Mesogloea is a thin jelly-like substance with no structure or cells. The medusa stage of Obelia species are common in coastal and offshore plankton around the world. At the growing ends of the main branches are immature club-shaped polyps. Digestion is both extracellular and intracellular. Obelia :V.S of Polyp Fig. Obelia is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. The asexually reproducing polyp and sexually reproducing medusa will be combined in the form of 'Cluster' and a polymorphic individual is developed. The statocysts act as organs of equilibrium. Striking as is the difference between polyp and a medusa, they are strictly homologous structures, and the more complex medusa is readily derived from the simpler polyp-form. The apex of the umbrella of medusa corresponds with the base of a hydranth. Medusae are carnivorous and the processes of their nutrition are essentially the same as in the polyp. Answer: (c) 6. In the endoderm layer are nerve cells and club-shaped gland cells which produce digestive enzymes. 14. It is a modified medusoid zooid. Below the hypostome is the stomach region of the polyp. Gastrozooid : It is a nutritive zooid. Cells generally pass in succession through a phase of rapid non-vacuolate division, slower vacuolate division, a vacuolate recovery phase, a pulsation phase, … 1.Bract : It is also called Hydrophillum'. The gonozooids are useful for reproduction. It is carnivorous and feeds upon aquatic crustaceans, nematodes and other worms. They alone take up nutrition in the colony. In order to be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population (one with random mating).. Three mechanisms may cause polymorphism: This is very easy … They are also known as blastostyles; Trimorphic: This polymorphic pattern bears an additional zooid called as dactylozooids along … Share Your Word File The polyp is protected in hydro theca, which is prolongation of the perisarc. When the bell tilts, the statoliths respond to the pull of gravity and stimulate the sensory bristles to which they are attached. Thus Haliste-mma shows the highest degree of polymorphic tendency in Coelenterates. From its base along tentacle will arise. Near the bulbs the ectoderm has pigment granules and nerve cells, they are often called ocelli and it is claimed that the ocelli are sensory to light, but more probably there are no ocelli, the pigment granules are accumulated excretory matter. a) Nectosome : It is the upper part of the coenosarc. The walls are two layered and highly muscular. This ensures an efficient division of labour between the severa individuals.. Furthermore, the muscular system is best developed around the bell margin and sub umbrella surface where the fibres form a radial and circular system. Firstly it must be made clear that alternation of generations as found in Obelia is simply an example of polymorphism, which may be defined as the ability of a single species of animal to exist under more than one form—in this instance as polyp and medusa. Explain the factors which cause dormancy. A. Anthozoa. Polymorphism refers to the occurrence of structurally and functionally more than two different types of individuals within the same organism. Gastrozooid: It is a modified polyp. Polymorphism in biology and zoology is the occurence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. In which of these the perisarc forms shelf like ring in Obelia The characteristic larva in coelenterates is (a) Oncosphere (b) Rhabditiform (c) Planula (d) Cysticercus. The endoderm lines the enteric cavity and the radial and circular canals. The gonads found in medusa are not formed in it but actually they are formed in the ectoderm of blastostyle which later on migrate into the medusa and become situated on its radial canals. For example, in Obelia shows polymorphism, the gastrozooids for feeding and the individuals capable of asexual reproduction only are the gonozooids, the blastostyles and medusae. The perisarc constitutes the exoskeleton and it covers the hydrorhiza, hydrocauli and their branches, and at the base of each polyp, it forms a clear, wine glass-shaped hydro theca. This phenomenon is called polymorphism. The individuals of the colony are called zooids. The occurrence of more than one type of structurally and functionally different individuals within a population is called polymorphism. The cavity of the vesicle is continuous with the enteron of blastostyle. Thus, a simple polyp or hydrula is formed which grows a hydrorhiza from its base, from which an Obelia colony is formed by budding. From the edge of the bell numerous small solid tentacles hang downwards. The medusa is free swarming. Dimorphic: It is simplest and commonest pattern of polymorphism ; They have only two types of zooids (gastrozooids and gonozooids) and the phenomenon is known as dimorphism.
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