Sponge reproduces asexually by fragmentation. During sexual reproduction, some cells become egg or sperm cells. After fertilisation, the zygote develops into a flagellated larva which swims, settles in a new place and grows into a sponge. Proterospongia is a connecting link between protozoa and porifera. In Hyalonema, root tuft consists of bundle of long anchoring spicules.
These may pass through the columella body axis as gastral cone. It is commonly known as glass rope sponge. Euspongia is commonly found is Mediterranean sea.
It is commonly known as Bath sponge. Amphiblastula is the hollow larva of Sycon etc. They are sessile, free swimming, radially symmetrical invertebrates and more complex than sponges. Cnidarians exhibit a blind sac body plan and are radially symmetric. They are more advanced than sponges in having true tissues. They are, however, acoelomate. Body wall consists of only two cell layers, the ectoderm and the endoderm, separated by a jelly-like mesoglea.
These animals are therefore diploblastic, that is, arising from two embryonic cell layers. Concept Builder Body wall in coelenterates with reference to Hydra. They are diploblastic animals i. These germ layers form the epidermis and gastrodermis.
A portion of body wall in longitudinal section magnified. The muscle processes contain a contractile fibril myoneme. They are most numerous on the tentacles, hypostome and basal disc. They receive and transmit impulses. They are present at the base of epithelio-muscle cells. They conduct impulses in all the directions.
They proliferate to form gonads. They are ectodermal in hydrozoa and endodermal in Scyphozoa and Anthozoa. They migrate to the tentacles through the mesoglea by means of amoeboid movements. Projecting cnidoblasts act as organs for offence and defence. The sac is a part of stinging apparatus, known as the nematocyst stinging structure. The cells are of following types : a Endothelio-muscle or nutritive muscle cells : They help in contraction of the body and nutrition. In the region of hypostome and mouth are found mucous gland cells.
Gland cells are absent in the tentacles and basal disc. Their digestion is intra and extracellular. Concept Builder 1. The green colour of Chlorohydra viridissima comes from alga Chlorella vulgaris Zoochlorella , that lives inside the gastrodermal cells of Hydra in symbiotic relationship.
Corallium rubrum red coral has been used widely in jewellery and known as red moonga. Tentacles of Hydra are hollow while that of obelia are solid. Thus, it is carnivorous. It cannot digest starch. Hence, development is direct. Following fertilization, the zygote forms a ciliated larva called Planula, which swims, settles and grows into a sessile polyp. Some cnidarians, like Hydra, do not have a medusa stage. Hydra has no larval form, no metagenesis. Both asexual and sexual forms are free living.
Hydra - Fresh water polyp e. Aurelia - the Jelly fish, e. This class has two types of Physalia - the Portuguese Moon jally, animal man-of-war. It is formed of calcium carbonate produced by some of its inhabitant, chiefly medreporarian corals. Coral reefs form stable marine ecosystems.
The coral reefs are of three kinds : i Fringing Reefs : The coral reefs lying close to the shores of some volcanic island or part of some continent are called the fringing reefs. Hawaiian is lands are an ideal example of permanent fringing reefs. The stretch of water of lagoon separates the barrier reefs from land. Australia's Great Barrier Reef is an example of such a reef which is about nautical miles long and 90 miles from sea shore. It may be complete or broken by a number of channels of which only a few are navigable.
Food that swims or is suspended in water is more plentiful than food that flies or is light enough to be suspended in air.
Beyond a certain depth there is not enough sunlight to support the algae. Body soft, delicate, transparent and gelatinous without segmentation. Polyp phase is absent in their life cycle, shape is typically spherical, pear shaped or cylindrical, flat in some. They are radially symmetrical, diploblastic, tissue level of organisation and devoid of cnidoblast cells. Tentacles may be present or absent. When present, the number of tentacles is 2. They are solid and possess adhesive cells called colloblasts lasso cells.
Digestion is both extracellular and intracellular. Bioluminescence the property of a living organism to emit light is well- marked in ctenophores. The animals move by cilia, which join together to form comb plates.
There are eight median combplates forming locomotor organs, hence organisms are called comb-jellies or sea- walnuts. Gastrovascular cavity is branched and opens to the exterior by stomodaeum. They are diploblastic animals but the mesoglea is different from that of cnidaria; it contains amoebocytes and smooth muscle cells and is comparable to a loose layer of cells. From this viewpoint, ctenophores may be considered as triploblastic.
Skeletal, circulatory, respiratory and excretory systems are absent. Nervous system is diffuse type. The presence of a special sense organ 'Statocyst' at the opposite end of the mouth aboral end is the characteristic of the members of this phylum.
All are hermaphrodite. Testes and ovary formed side by side from endoderm of digestive canals. Asexual reproduction doesn't occur. They reproduce only by sexual means. Fertilization is. Development is indirect and an immature ciliated stage called 'cydippid larva' is found in some forms. Concept Builder Word roots and Origins : a Colloblasts from the Greek kolla meaning "glue" and blastos meaning "bud".
Self Assessment Q. The flat worms are mostly parasites but some are free living e. They are acoelomate, triploblastic, bilaterally symmetrical and dorsoventrally flattened animals. They have organ system level of organisation. Body is not segmented except in class Cestoda false segmentation.
Body is covered with a cellular, syncytial, one layered, partly ciliated epidermis; while in parasitic trematodes and cestodes, epidermis is lacking and the body is covered with cuticle. Exoskeleton and Endoskeleton are completely absent.
However hooks, spines, suckers in parasitic form , teeth or thorns may be present which act as adhesive organs. The space between the body wall, alimentary canal and other organs is filled with a peculiar connective tissue called the parenchyma. It helps in transportation of food materials. Digestive system is totally absent in tapeworms, so they absorb food directly through body surface. In Trematoda and Turbellaria, it consists of mouth, pharynx and blind intestine anus absent. Respiratory and circulatory systems are absent.
Excretory system consists of single or paired protonephridium with flame cells. Nervous system is primitive. The main nervous system consists of a pair of cerebral ganglia or brain and one to three pairs of longitudinal nerve cords connected to each other by transverse commissures.
This type of nervous system is called ladder like nervous system e. Sense organs are of common occurrence in Turbellaria but these are greatly reduced in parasitic forms.
Sexes are united, i. Asexual reproduction by fission occurs in many fresh water forms like Turbellarians. In majority of forms, eggs are devoid of yolk but provided with special yolk cells and are covered by egg shell. Cross fertilization in trematodes and turbelleria and self-fertilization in cestodes is very common.
Fertilization is internal. Development indirect with many larval stages. Life cycle complicated, involves one or more hosts. It is well marked in some flat worms like Planaria. Turbellaria Trematoda Cestoda — Free living fresh water or — Endo-Parasite, known as flukes, — Endo-Parasite Intestinal parasite, marine known as Planarians or or flat worms.
Eddy worm. No epidermis in epidermis Rod shaped Rhabdites Fine spines No epidermis in adult. Alimentary canal is absent. Alimentary canal- from body surface. Alimentary present. Branched branched. Dugesia - Planaria e. Shows multiplication in larva stage namely — Oncosphere, Hexacanth, Bladderworm and Cysticercus.
Causes disease Taemiasis or Cysticercosis. What is their proper sequence? They are circular in cross-section. Examples: Ascaris, Wuchereria, Enterobius, Trichuris.
Rhabditis is a free living roundworm. Class : Rotifera. Examples: Wheel worms. General characters of Phylum Annelida 1. The organisms are triploblastic, bilaterally symmetrical, coelomates with organ system level of body organization and are metamerically segmented. Body wall has an epidermis of columnar epithelium coated externally by moist albuminous cuticle and with circular and longitudinal muscle fibres.
Chitinous setae, aiding in locomotion, mayor may not be present on fleshy parapodia; absent in leech. Annelids are the first animals to have a true schizocoelic coelom. Coelom is divided by septa into compartments. The coelomic fluid act as a hydrostatic skeleton. Digestive system is complete and digestion is extracellular. Respiration by moist skin cutaneous respiration or through gills Branchial respiration.
Blood vascular system is usually closed. Respiratory pigments, either haemoglobin or erythrocruorin, are dissolved in blood plasma. Free amoeboid blood corpuscles are present, butthere are no RBCs. Nephridia are the excretory organs. The nervous system consists of a nerve ring and asolid, double, mid-ventral nerve cord with ganglia and lateral nerves in each segment.
Sensory organs include tactile organs, taste buds, statocysts, photoreceptor cells and eyes with lenses. The sexes may be separate e. Development is mostly direct e. There is indirect development in Nereis. Larva, when present is trochophore. Almost all are 1. Most of the members 1. Aquatic, terrestrial, 1. All Marine 1. Without external marine are terrestrial, but ectoparasite and and internal some are aquatic. Cephalisation is 2. Cephalisation absent.
Cephalisation 2. Cephalistion 2. Seate are rare and more distinct. Setae numerous 3. Number of seatae is 3. Parapodia and 3. Parapodia and prostomium or limited seatae are absent. Clitellum absent 4. Clitellum is present 4. Clitellum develop 4. Clitellum absent. Polygordius — clamworm e. NEREIS Inhabits in sea - shore between tide mark, burrower, nocturnal, carnivorous, gregarious, fertilization - in sea. During breeding body divides in two parts.
Anterior asexual part - Atoke and posterior sexual portion Epitoke. This change is known as epitoky. The largest class is insecta with , species.
They are triploblastic, coelomate and bilaterally symmetrical animals. The body cavity is full of haemolymph blood and it's known as haemocoel. The true coelom is restricted to gonads. The body is covered by chitinous cuticle, which forms the exoskeleton which is shed at intervals i. They have a segmented body, each segment bearing a pair of jointed appendages covered by a jointed exoskeleton.
Chitinous exoskeleton is secreted by the underlying epidermis. The body is divided into head, thorax and abdomen. In some cases, the head and thorax is fused to form cephalothorax. In insects, the thoracic segments have legs and wings, the abdomen has no legs in insects.
Respiratory organs are gills, book gills, book lungs or tracheal system. Excretion takes place through green glands or malpighian tubules since nephridia are absent. Sensory structures in arthropods are antennae for perceiving odour, eyes, statocysts or balance organs and sound receptors in chirping crickets and cicadas.
Eyes are simple or compound. In honey bees, butterflies, moths and some other insects, the gustatory receptors are present on their feet.
The heart is dorsal and circulatory system is open. The central nervous system consists of paired pre-oral ganglia connected by commissures to a solid double ventral nerve cord. In land arthropods, the fertilization is always internal. Arthropods are mostly dioecious, oviparous.
In some like the scorpion, the eggs hatch within the female body. They bring forth the young ones alive.
They are viviparous. Development is direct or indirect. Advancement Over Annelida 1. Distinct-head in all species. Jointed appendages serving a variety of functions. Jointed exoskeleton for protection and muscle attachment. Striped muscles arranged in bundles for moving particular body parts.
Special respiratory organs such as gills, trachea, book lungs in majority of cases. Well developed sense organs such as compound eyes, statocysts, auditory organs, taste receptors etc. Endocrine glands and pheromone secretion for communication. Class 1. Sexual dimorphism is also seen. Tiny crustaceans such as Oaphnia and Cyclops act as zooplanktons which form important link in the food chain in water. Class 2. Chilopoda i Body is long, segmented and divisible into head and trunk.
The first pair of legs are modified into poison claws. Diplopoda i Body is divisible into head, thorax and abdomen.
Class 4. Insecta Hexapoda [Largest number of species] i Body is divisible into head, thorax and abdomen. For example, mesothoracic wings which are thick and leathery are called tegmina and metathoracic wings are membranous in cockroach.
Wings may be absent in same insects. No respiratory pigments. Uric acid is chief excretory waste. Maggot is the larva of Housefly. Pheromones are chemicals secreted outside the body and perceived as smell by other individuals of same species. They help in communication amongst the organisms of the same species. Arachnida i The body is usually divisible into cephalothorax and abdomen.
These classes are Onychophora and Merostomata. Peripatus is an important example of the class onychophora which has characters of phylum Annelida and Arthropoda. Umulus, the king crab or Horseshoe crab is an example of class Merostomata which respires with book gills.
A living fossil is a living animal of ancient origin with many primitive characters. Peripatus is considered as connecting link between annelida and arthropoda as it has unjointed legs and breathes by trachea. Terga are dorsal plates whereas sterna are ventral plates of exoskeleton. Arthrodial membranes join the different sclerites.
Halters are drumstick shaped, second pair of reduced wings of housefly and mosquito which helps in balancing. Eggs of Culex are cigar shaped; they are laid vertically on the surface of water in clusters; airfloats are absent; whereas in Anopheles eggs are boat shaped, laid singly and horizontally; they have airfloat.
Larva of Culex is bottom feeder whereas larva of Anopheles is surface feeder. So, they can be distinguished with the help of sitting posture. In Spider, Spinnerets are present anterior to the terminal anus.
They produce silken thread. Von Frisch described the process of communication of food source in honey bees. Insecticides sprayed over the mosquitoes desensitize their nervous system as well as chemoreceptors and mechanoreceptors ofthe antennae.
Johnston's organs are present on antennae of mosquitoes. The life cycle is generally accompanied with metamorphosis. Larvae and adults may show different feeding habits and occupy different habitats.
Insects like bees, wasps, beetles, moths and butterflies are good pollinators for important crops. Ants, termites and locusts are eaten by Chinese and Indians; Eggs of aquatic bugs are used as food by Mexicans; Ox-warbles are eaten by Red Indians. Dragon flies feed on the larvae of mosquitoes Glow worm Firefly shows bioluminescence.
Adult Culex and Anopheles can be distinguished with the help of Sitting posture. The insects may be divided into five groups on the basis of their mode of development. Ametabola insects — metamorphosis absent.
The young ones resemble adult. Lepisma Silver fish 2. Cockroach, Grasshopper, Locusts etc. Hemimetabola insects — incomplete metamorphosis. Habitat of young ones is different from adults. Dragon flies Naiads aquatic but adults aerial 4. House flies, Butterflies, Mosquitoes etc. Blister beetle. The radula is protruded from the mouth and worked back and forth to rasp the food into fine particles. Respiratory pigment is haemocyanin. Another excretory organ called Keber's organ Pericardial gland is also present in Unioalongwith paired organ of Bojanus.
Conceptual Questions Q. Gastropods move slowly and therefore need small amounts of energy and oxygen. Thus, their needs can be met byan open circulatory system. By doing so, the oyster makes these particles less irritating. Shell - Absent. Radula — Present for digging lie on same side.
Redula-absent and partly into 8 or 10 sucker Radula - Present e. Neomenia Larva-Trochophore e. Locomotion is by expelling e. Pinctada-Pearl oysters. Jet propulsion. Living fossils e. Pila-Apple-snail Ink glands in some squids Connecting link of Shell used in but-tons for offense and defense. Annelida and When the squid is attacked, it Mollusca and only emits a cloud of inky fluid segmented molluscs through its siphon.
This with nephridia. Animal Kingdom Non-Chordata 36 e. Sepia-Cuttle fish 10 arms having Chromatophores. Similarities with chordates : i They have tube within tube type of body plan which has evolved along deuterostomic evolutionary line.
The other characters are : 1. The symmetry is bilateral in larvae but pentamerous radial in adults. Many echinoderms bear a number of calcareous spines on their body surfaces called tubercles. Between the spines, there are pincer like structures called pedicellariae to keep the surface clean.
Pedicellariae are made of three calcareous plates. Two calcareous valve like structures in the form of jaws resting upon a basal calcareous plate. Between the spines, there are finger like processes called dermal branchiae which help in respiration.
There is no distinct anterior and posterior end i. Haemal and Perihaemal Systems: Instead of blood vascular system, there are present haemal and perihaemal systems which are of coelomic origin. Thus the so called circulatory system is open type. The so called blood is often without a respiratory pigment.
There is no heart. Respiratory Organs : Gaseous exchange occurs by dermal branchiae or papulae in star fishes, peristominal gills in sea urchins, genital bursae in brittle stars and cloacal respiratory trees in holothurians. Exchange of gases also takes place through tube feet.
Excretory organs : Specialized excretory organs are absent. Nitrogenous wastes are diffused out via gills or dermal branchiae. Ammonia is chief excretory matter. Sexes are separate. Reproduction is sexual.
Fertilization is usually external. Development is indirect with free-swimming larva. The coelom is lined externally by a parietal epithelium parietal peritoneum and internally by a visceral or splanchnic epithelium visceral peritoneum. The peritoneum surrounds all the internal visceral organs, including the alimentary canal. In other words, all the internal organs are retroperitoneal i. Thus, coelom is also called as the perivisceral cavity.
The coelom contains coelomic fluid and constitutes one or more perivisceral spaces around the heart, alimentary canal and other organs. Coelom is divided into fluid filled compartments by transverse partition called septa which extend from the annuli of the bodywall to the alimentary canal.
The wall of the septa is perforated, through which coelomic fluid communicates from one compartment to another. The coelom communicates with the exterior by two sets of ducts namely nephridia and coelomoduct.
Nephridia are ectodermal tubes that remove water and excretory waste while coelomoduct are mesodermal tubes which usually open into the coelom at one end while the other end communicates with the exterior.
However, in some coelomates like arthropods and molluscs, the coelom is reduced or absent in adult, but is present in the embryo. The visceral organs are surrounded by the haemocoel. The haemocoel reduces the coelom to small cavities around the heart pericardium , gonads and kidney. In these animals, the haemocoel is called the primary body-cavity while the coelom is called the secondary body cavity.
Coelom surrounds the internal organs and thus protect them from external shocks. It serves as a hydrostatic skeleton to assist in locomotion and maintaining shape of the body. It provides flexibility to the body. The internal organs in coelomate animals become large and are able to perform movements freely of their own. It helps in removing excretory waste from the body. Helps in the transportation of gases and nutritive materials from one part of the body to the other.
In some animals, it keeps the body wall moist to facilitate respiration and to destroy bacteria and other harmful micro-organisms. Acts as a site for gamete maturation and brooding of embryos. Schizen: to split; koilos: hollow The coelom arises from the splitting up of the mesoderm Fig.
Enteron:gut; koilos: hollow Coelom arises by the outpocketing of the archenteron in the initial separation of the mesoderm from the endoderm. In simple words, pouches arise from the archenteron, which fuse together to form a coelom Fig. Many theories have been put forward but only four of them are of importance. Some of these cells would form the peritoneum.
The acoelomate flatworms, thus, form the basic group in the evolution of bilateral animals. The schizocoel mode of coelom formation in the embryonic development of annelids and molluscs would claim as supporting evidence of this theory. However, the evolution of coelom is not related to gonads or endodermal pouches of lower forms. This theory argues that the coelom evolved from the gastric pouches of some cnidarian ancestors, such as anthozoans, or scyphozoans. These gastric pouches separated out from the main gastric cavity to form the coelomic pouches.
This theory proposes that all bilateral animals are basically coelomate and that acoelomate forms like flatworms are secondarily derived from coelomate ancestors by the loss of the cavity. The enterocoelous mode of coelom formation in the embryogeny of echinoderms, hemichordates and chordates is the main supporting evidence of this theory. The enterocoelous theory has never gained much importance because it is difficult to postulate functional steps that have led to a change from coelomate to acoelomate and from bilateral to radial symmetry.
In contrast, the ancestral position of flatworms among the bilateria and the primitive nature of the acoelomate body plan has been widely accepted. Moreover, the gastric pouches occur in the more advanced cnidarians such as Anthozoa and Scyphozoa, which are not suitable for ancestral types. Also, the enterocoelous theory of coelom origin is associated with the origin of metameric segmentation, an association imposing severe restrictions on the theory.
It regards the coelom as the cavity of an expanded gonad and its origin is based on the common association between the gonads and the coelomic epithelium. Bergh believed that coelom initially arose in a segmented condition by enlargement and cavitation of the gonads after the release of gametes Fig. One of the main drawback of this theory is that it closely links the origin of coelom with the origin of metameric segmentation and hence it is difficult to account for the unsegmented coelomates.
There is no evidence that the unsegmented coelomates have originated from the segmented ancestors. This theory has no embryological support because gonads donot arise before the coelom.
The coelom originated as an expanded nephridium. This theory however, was never taken seriously because protonephridia has been described in coelomates and also excretory organs are absent in some coelomates like echinoderms.
Meta: after ; Mere: part The serial segmentation of the body along an anterior- posterior axis is called metamerism. Each segment is known as a metamere or somite. True metamerism occurs in annelids, arthropods and most chordates. A typical segmented animal has a specialized anterior head or acron and a posterior pygidium or telson with varying number of intermediate segments. Metamerism is always limited to the trunk region of the body. The head bearing the brain and sense organs and the pygidium is not a metamere.
The growth region in these metamerically segmented animals is localized to the region in front of the pygidium.
Thus, new segments in them arise from just in front of the pygidium while the oldest ones are present just behind the head. In these metamerically segmented animals the appendages, nerves, ganglia, muscles, nephridia, gonads, coelomic cavities and transverse blood vessels are repeated within each segment. The segments are also marked by constriction of the body wall musculature.
The ideal condition of exactly similar segments is known as homonomous segmentation. It is not present in any existing animals because a few of the anterior segments are always specialized to form the head.
The closest approach to homonomous condition is seen in Polychaetes, in which all the segments in between the head and pygidium are similar Fig. Generally, the segments of particular region are lost or fused together and modified for special functions.
This is known as heteronomous segmentation. The anterior segments are united together to form the head that bears the nervous, sensory, and feeding structures, a process called cephalization.
The segments of the other region are also specialized resulting in differentiated parts of the body. The adults of arthropods and chordates show incomplete or heteronomous metamerism. There are two types of segmentation: 1. Mesodermal: beginning in the mesoderm and proceeding outwards e. Superficial: begins externally from the circular surface, then proceeds inwards, often involving only the body wall musculature e. The kind of segmentation encountered in tapeworms is mesodermal but differs from true segmentation as seen in annelids.
In annelids and arthropods new segments are formed at the posterior end while in tapeworm the neck is the zone of proliferation. It is believed that metamerism has evolved twice in the animal kingdom: 1. In annelids as an adaptation for burrowing.
In chordates as an adaptation for undulatory swimming. Segmentation in them was probably an adaptation for an undulating mode of swimming. This theory was supported by Hyman and Goodrich. They observed such serial repeatition of organs in some elongated turbellarians and nemerteans which later crystallized into metameric segmentation.
Metamerism has evolved from the fundamental radial organization of the Actinians class Anthozoa: phylum Cnidaria by the separation of four gastric pouches or enterocoelic pouches from the central gut Fig. According to the believers of this theory, the gastric pouches in these cnidarians were linearly arranged and not in a circular fashion. According to this theory, all bilateral metazoans were originally segmented and coelomate and that the acoelomate unsegmented groups Platyhelminthes, and Nemerteans have secondarily lost these characters.
According to this theory, some non-segmented ancestors divided repeatedly by transverse fission or by asexual budding producing a chain of zooids or sub-individuals. These zooids remained united end to end due to their incomplete separation. With the passage of time, these sub-individuals gradually became integrated into a complex individual, both morphologically and physiologically.
A segmented animal, thus, is a chain of completely coordinate sub-individuals Fig. The major drawback of this theory is that the reproduction by fission is usually confined to sessile animals whereas the ancestors of metamerically segmented animals were probably free swimming. Another objection is that the sequence of zooid formation is never serial, fission always occurs in the middle of the chain e. Platyhelminthes, and strobilae of Scyphozoans.
However, in cestodes, the proglottids are serially arranged but in the reverse order i. The formation of metameric segmentation was mainly as an embryological accident. Clark suggested that the ancestors of phylum Annelida were elongated coelomate animals which were burrowers. The coelom gave a hydrostatic skeleton to these animals while the development of septa and metameric segmentation allowed only a part of the body to contract while other parts in the longitudinal axis relaxed.
The locomotion can be more coordinated and controlled if the action of body-wall muscles are localized. Metamerism permits such localization and also accounts for the evolution of this condition in annelids. This leads to regional specialization of segments thus leading to rapid evolution of high grade of organization. The simplest of this regional specialization is seen in annelids in which the body may be weakly divided into head, thorax and abdomen. These three divisions are more prominent in arthropods.
In higher vertebrates, even the segmental arrangement of muscles is obscured by regional specialization. Thus, primitiveness of an animal, to some extend, can be determined by the degree of segmentation it displays.
Metamerism helps in locomotion in several ways. It facilitates lateral movement of the body. Since metameric segmentation results in compartmentalization of the body, the coordination of muscular action can be restricted to a few segments at a time thereby increasing the locomotory efficiency. The origin of metazoa is based on this assumption. Later, the theory was modified by Metschnikoff and Hyman According to this theory the ancestors of the metazoans are the flagellates.
The ancestral metazoan probably arose from a spherical, hollow, colonial flagellate. The colony possessed a distinct anterior-posterior axis with monoflagellate cells on the outer surface.
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