ZOOLOGY-SEMESTER-I-Unit-I

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Phylum Protozoa General characters The Protozoa mark the beginning of animal life. Being the simplest in structure, protozoa are regarded most primitive or first animals (Gre. Protos-first, zoon- animal) of nature.  Protozoa may be defined as microscopic & acellular animalcules, without tissues and organs, having one or more nuclei, but no nucleus ever in charge of a specialized part of cytoplasm.  They exist either single or in colonies which differs from a metazoan in having all the individuals alike except when engaged in reproductive activities.  They are usually microscopic animalcules, ordinarily not visible without a microscope, acellular found all over the world as they exhibit a great range of structural complexity and adaptations for all types of environmental conditions.  Protozoans occur wherever moisture is present. Hence, they occur in seawater, in all types of fresh water & in the wet soil. Thus protozoans exhibit mainly two modes of life free living inhabiting fresh & salt water & damp places, parasitic living as ecto & endoparasites. There are many protozoa which are commensal & mutualistic.  Majority of protozoa are solitary & some form colonies, the solitary forms are mostly free-living, whereas colonial ones are often attached. (Some colonial forms (Volvox) attain such degree of cellular interdependence that they approach a true multicellular level of structure.  Body symmetry none,  bilateral,  radial. Or spherical,  oval,  bell shaped,  spindle shaped,  slipper like or irregular.  Body naked or bounded by a pellicle, (theca, Lorica or silicious shell) often provided with simple to elaborate shells or exoskeletons.

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 Body form usually constant, varied in some. While changing with environment or age in many.  Single cell body performs all essential & vital activities, which characterize the animal body, hence only sub-cellular physiological division of labour.  Locomotor organelles are  Finger-like Pseudopodia (Sarcodina) or  Whip-like Flagella (Mastigophora) or  Hair like Cilia (Ciliate) or  Absent(Sporozoa)  Nutrition  Holozoic (animal-like),  Holophytic (plant like),  Saprozoic or Parasitic with or without definite oral & anal aperture.  Digestion occurs intracellularly inside food vacuoles.  Respiration and Excretion through general surface (diffusion) or through contractile vacuoles to remove soluble water matter through osmoregulation. In some forms excretion occurs through a temporary opening in ectoplasm or through permanent pore (cytopyge)  Reproduction Asexual by  binary or multiple fission and budding and Sexual by  conjugation of adults (hologamy) or by fusion of gametes (syngamy) or (copulation, autogamy, paedogamy)  Life history often complicated with alternation of asexual and sexual phases.  Encystment commonly occurs to help in dispersal as well as to resist unfavourable conditions of food, temp. and moisture. The single celled individual not differentiated into somatoplasm and germplasm, therefore exempted from natural death which is price paid for body.

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About 50,000 known species. Nucleus is the seat of control of all vital activities of protozoan body. This is shown by the fact the denucleated organism soon dies. Nucleus is therefore most important organelle of every protozoan as indeed every metazoan cell. Classification of Protozoan Phylum protozoa is a large and varied group and poses a number of problems in its classification,

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Classification of Protozoan Phylum Protozoa is a large and varied group and poses a number of problems in its classification. The following classification of Protozoa is based on the scheme given by the committee on taxonomy and taxonomic problems of the society of Protozoologists and mainly proposed by B.M. Honigberg and others (1964). It divides Protozoa first into 04- sub phyla:- I. Sarcomastigophora II. Sporozoa III. Cnidospora and IV. Ciliophora

Brief outline of sub phylum Sarcomastigophora I. Sarcomastigophora (3 super classes) Super Class A. Mastigophora (Flagellate) 2 classes 1. Phytomastigophora (Phytoflagellata), 2. Zoomastigophora (Zooflagellata) Super Class B. Opalinata Super Class C. Sarcodina (Rhizopoda) 03 classes Class 1. Rhizopodea, 3 subclasses Sub class (a) Lobosia, Sub class (b) Filosia, Sub class © Granuloreticulosia Class 2. Actinopodea, 4 sub class Sub Class a. Heliozoia, Sub Class b. Radiolaria Sub Class c. Acantharia, Sub Class d. Proteomyxidia Class 3. Piroplasmea

Sub phylum I. Sarcomastigophora Locomotor organelles pseudopodia or flagella or both. Nuclei of one kind (monomorphic). This subphylum has 03- Super Classes

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Super Class A. Mastigophora (Flagellate) Simple, primitive, with firm pellicle (protozoan body wall composed of cell membrane, cytoskeleton and other organelles). Locomotor organelles flagella. Nutrition autotrophic or heterotrophic or both. It has got 02 classes 1. Phytomastigophora (Phytoflagellata) Chlorophyll bearing chromotophores present. Nutrition mainly holophytic by phototrophy. Reserve food starch or paramylon. Flagella 1or 2, sometimes more. This class is divided into 08 orders bearing following popular species Euglena. Volvox, Chlamydomonas etc. 2. Zoomastigophora (Zooflagellata) Chlorophyll or chromatophores absent. Mostly parasitic. Nutrition holozoic or saprozoic. Reserve food glycogen. Flagella one to many. It is divided into 09 orders bearing well known species like Trypanosome, Leishmania. Trichomonas, Giardia etc. Super Class B. Opalinata Entire body covered by cilia like flagella. Nuclie 02 to many, monomorphic. Reproduction by symmetrogenic binary fission or by syngamy of anisogametes. Parasitic mainly in frogs and toads eg. Opalina, Zelleriella Super Class C. Sarcodina (Rhizopoda) Body mostly amoeboid without definite pellicle, some with a skeleton of some kind.

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Locomotion by pseudopodia. Nutrition holozoic or saprozoic. This Super Class has 03 classes. Class 1. Rhizopodea Pseudopodia as Lobopodia, Filopodia or Reticulopodia, without axial filament. They are generally creeping forms This Class has 03 Sub Classes Sub class (a) Lobosia Pseudopodia as lobopodia Eg., Amoeba, Entamoeba. Pelomyxa, Arcella, Euglypha, Sub class (b) Filosia Pseudopodia as Filopodia. Naked or with a shell with single aperture. eg, Allogromia, Penardia (naked) Sub class © Granuloreticulosia Pseudopodia delicate granular reticulopodia eg, Elphidium. Class 2. Actinopodea Pseudopodia mainly axopodia with axial filament radiating from a spherical body It has 04 Sub Classes Sub Class a. Heliozoia Spherical protozoans called sun-animalcules Pseudopodia (axopodia) radiating. Naked or skeleton of siliceous scales or spines eg, Actinophrys, Actinosphaerium Sub Class b. Radiolaria Body naked or with perforated chitinoid central capsule separating ectoplasm from endoplasm.

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Reticulopodia, axopodia or filopodia Skeleton mostly of silicious spicules or of strontium sulphate Eg. Collozoum, Thalassicola Sub Class c. Acantharia Imperforate non chitinoid central capsule without pores Skeleton of strontium sulphate Pseudopodia are axopodia Eg, Acanthometra Sub Class d. Proteomyxidia Pseudopodia are filopodia Mostly parasites on algae Eg. Vampyrella, Pseudospora Class 3. Piroplasmea Small round, rod shaped or amoboid parasites in red blood cells of vertebrates eg. Babesia (formely included with sporozoa but its species do not produce spores) Note Axopodia: fine needle like pseudopodia that contains a central bundle of microtubules Filopodia: pseudopodia that is slender, clear and sometimes branched Lobopodium: pseudopodia that is rather wide with round or blunt tips is commonly tubular and is composed of both ecto and endoplasm Reticulopodium: pseudopodium that forms thread like branched mesh and contain axial microtubules. Axial filament contractile element in the tail of sperm

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Brief out line of sub phylum Sporozoa Subphylum II Sporozoa 03 classes Class 1. Telosporea 02- sub classes Sub class (a) Gregarinia Sub class (b) Coccidian Class 2. Toxoplasmea Class 3. Haplosporea

Subphylum II Sporozoa  Locomotor organelles absent. Spores usually present.  Exclusively endoparasites and incapable of active life outside their hosts.  Cilia or flagella may be present in gametes.  Asexual reproduction by multiple fission and sexual by syngamy. 03 classes  Class 1. Telosporea  Spores without polar capsules and filaments naked or encysted.  Locomotion by gliding or body flexion due to absence of pseudopodia.  Adult trophozoites with one nucleus.  Reproduction both sexual and asexual. Eg; Monocystis, Plasmodium, Eimeria 02- sub classes . Sub class (a) Gregarinia  Mature trophozoites large, extracellular in hosts gut and body cavities.  Each spore produces 08 sporozoites.  Parasites of invertebrates. Eg; Monocystis, Gregarina . Sub class (b) Coccidian  Mature trophozoites small and intracellular.  Each oocyst produces many sporozoites.  Blood or gut parasites of vertebrates.

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Eg; Eimeria, Isospora. Plasmodium  Class 2. Toxoplasmea  Spores absent. Only asexual reproduction by binary fission.  No flagella or pseudopodia at any stage.  Cysts with many naked sporozoites. Eg. Toxoplasma, Sarcocystis.  Class 3. Haplosporea  Spore case present. Only asexual reproduction and shizogony takes place.  Flagella absent but pseudopodia may be present.  Parasites of fish and invertebrates. Eg; Ichthyosporidium, Haplosporidium.

Brief outline of sub phylum Cnidospora Sub phylum III Cnidospora 2 classes Class 1. Myxosporidea Class 2. Microsporidia

Sub phylum III Cnidospora Spore formation occurs throughout life and polar filaments present. Zygote gives rise to one or more trophozoites without sporogony. Adult trophozoites has many nuclei. 2 classes  Class 1. Myxosporidea  Spores large, developed from several nuclei.  Spores with two or three valves.  Parasites mostly in fishes.  Polar capsule present. Eg. Myxidium, Ceratomyxa.  Class 2. Microsporidia

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 Spores small, developed from one nucleus.  Spores with a univalved membrane.  Intracellular parasites in arthropods and fishes.  Polar capsule absent or present with 1 or 2 filaments. Eg; Nosema.

Brief out line of Sub phylum Ciliophora Subphylum IV Ciliophora 01 class Class Ciliata (Infusoria) 04 sub classes Sub class(a) Holotricha Sub class(b) Peritrica Sub class© Suctoria Sub class (d) Spirotrichia

Subphylum IV Ciliophora  Presence of cilia as locomotor and feeding organelles at some stages in life cycle. (being simple to compound for feeding and locomotion).  Nuclei of 2 kinds(dimorphic), a trophic macronucleus and a reproductive micronucleus.  One or more contractile vacuoles are present in fresh water forms.  Reproduction asexual by transverse binary fission, conjugation also takes place with fusion of nuclei.  Nutrition mixotrophic or heterotrophic.  They usually have cytostome. Only 01 class  Class 1. Ciliata (Infusoria)  Locomotor organelles numerous hair like cilia, present throughout life.  Definite mouth (cytostome) and gullet present except in few parasitic forms. Anal aperture (cytopyge).  One or more contractile vacuoles present even in marine and parasitic forms.

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 Mostly two kinds of nuclei, large macronucleus and smaller micronucleus.  Nutrition holozoic.  Mostly free living in fresh water, marine water but parasitic forms also occur. eg; Vorticella, Bursaria, Paramecium, Blantidium. 04 Sub classes . Sub class (a) Holotricha  Body cilia simple and uniform.  Buccal cilia mostly absent. It has 6 orders with eg; Coleps, Didinium, Prorodon, Dileptus, Blantidium. Colpoda, Spirochona, Lobochona, Hyalophysa, Anoplophyrya, Maupasella, Colpidium, Paramecium. . Sub class (b) Peritrica  Adult without body cilia.  Apical end with buccal cilia. 1 order with eg; Vorticella, Carchesium. . Sub class© Suctoria  Sessile and stalked body.  Young with cilia, adult sectorial tentacles. 1 order with eg; Acineta, Ephelota, Podophyra. . Sub class (d) Spirotrichia  Reduced body cilia.  Buccal cilia well marked. 3 orders with eg. Stentor, Bursaria, Spirostomum, Strombidium.

END OF PROTOZOAN CLASSIFICATION

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Brief out line of sub phylum Sporozoa Subphylum II Sporozoa 03 classes Class 1. Telosporea 02- sub classes Sub class (a) Gregarinia Sub class (b) Coccidian Class 2. Toxoplasmea Class 3. Haplosporea

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Brief outline of sub phylum Cnidospora Sub phylum III Cnidospora 2 classes Class 1. Myxosporidea Class 2. Microsporidia

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END OF PROTOZOAN CLASSIFICATION

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Locomotor organelles and Locomotion in Protozoa Locomotor organelles in Protozoan include Pseudopodia, flagella, cilia and pellicular contractile structure. I) Pseudopodia: or false feet are temporary structures formed by the streaming flow of cytoplasm. Sarcodina move with these structures. On the basis of form and structure, pseudopodia are of four types. 1. Lobopodia: These are lobe- like pseudopodia with broad and rounded ends, as in amoeba. These are composed of ecto and endoplasm. Lobopodia move by pressure flow mechanism. 2. Filopodia: These are more or less filamentous pseudopodia, usually tapering from base to pointed tip, as in Euglypha. Unlike lobopodia, the filopodia are compound of ectoplasm only. Sometimes they may branch and form simple or complex networks. 3. Reticulopodia: or (rhizopodial or myxopodia) are also filamentous. Filaments are branched and interconnected profusely to form a network. This type occurs in forminiferans (eg; Globigerina). Reticulopodia disply two- way flow of cytoplasm. 4. Axopodia: These are more or less straight pseudopodia radiating from surface of body. Each axopodia containing a central axial rod which is covered by granular and adhesive cytoplasm. Like reticulopodia, axopodia also display two -way flow of cytoplasm. Axopodia are characteristic of heliozoans, such as actinosphaerium and actinophrys. II) Flagella: are locomotory organelles of flagellate protozoa, like euglena, trypanosome etc. These are thread like projections on the cell surface. A typical flagellum consists of an elongate, stiff (axoneme), enclosed by an outer sheath. In axoneme, nine longitudinal peripheral paired fibers form a cylinder, which surrounds the two central longitudinal Fibers, enclosed by a membraneous inner sheath.

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Each of peripheral pairs bears a double row of short arms. Axoneme arises from a basal granule, the blephaeroplast or kinetosome. Mostly, it is a cylindrical body formed by bases of peripheral fibers. Blephaeroplast are derived from centrioles as the two structures are homologous. Fibers of axoneme remain embedded in a fluid matrix. In between outer ring of peripheral fibers and inner ring of central fibers, mostly occur 09 fibers. In certain groups of mastigophora are found flagellar appendages or mastigonemes extending laterally from outer sheath. No. and arrangement of flagella vary in mastigophora from one to 08 or more. Free living species have usually one or two, while in parasitic species, the number ranges from one to many. III) Cilia: characteristic of ciliata, resembles flagella in their basic structure. These are highly vibratile small ectoplasmic processes. Electron microscope reveals the presence of an external membraneous sheath and enclosing the fluid matrix. Running along entire length of body of cilium are nine paired peripheral fibers and central fibers, all embedded in structure less matrix. Central fibers are enclosed within a delicate sheath. In between outer and inner fibre rings are present nine spoke-like radial lamellae. In addition to these, one sub- fibre or microfiber of each peripheral pair bears a double row of short, projections called arms all pointing in same directions. Each cilium arises from a thickened structure called basal granule, basal body or blepharoplast. According to Lenhssek and Henneguy (1898), basal granules show nine peripheral sub fibre triplets, each disposed in a twist like fashion. In many species, cilia become fused variously forming compound organelles such as undulating membranes (pleuronema), membranelle (Vorticella) and cirri (Euplotes). IV) Pellicular contractile structure: in many protozoa are found contractile structures in pellicle or ectoplasm called

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myonemes, these may be in form of ridges and grooves (e,g; Euglena), or contractile myofibrils (e.g; larger ciliate) or microtubules (e.g; Trypanosoma).

Methods of locomotion Basically there are four known methods by which protozoa move. i) Amoeboid movement, ii) Flagellar movement, iii) Ciliary movement, iv) Metabolic movement Speed of locomotion varies from 0.2microns to 3microns per second in amoeboid forms, 15microns to 300microns in flagellates and 400microns in ciliate. i) Amoeboid movement: it is characteristic of all sarcodina and certain mastigophora and sporozoa. It consists in the formation of pseudopodia by streaming flow of cytoplasm in direction of movement Locomotion by pseudopodia is possible only over a surface. We still do not know precisely about the mechanism involved in formation of pseudopodia but the most convincing theory at present is that it depends upon active contraction of ectoplasmic tube (plasmagel) at posterior end of body. This leads the endoplasm (plasmasol) to flow forward into expanding pseudopodium. This process involves continuous solation at posterior end and gelation at anterior end. This theory is called sol gel or change of viscosity theory by Mast and Pantin (1925). It was further developed by Goldacre and Lorch (1950) and by Allan and Rosalansky (1958). ii) Flagellar movement: is characteristic of mastigophora which bears one or more flagella. The flagella need liquid medium for movement or locomotion. 03 types of flagellar movements have been recognized.

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1. Paddle stroke: Ulehla and Krijsman (1925) observed that common movements of a flagellar is sideways lash, consisting of an effective down stroke with flagellum held out rigidly and a relaxed recovery stroke in which flagellum strongly curved is brought forward again. As a result animal moves forward gyrates and is also caused to rotate on its longitudinal axis. 2. Undulating motion: wave-like undulations in flagellum, when proceed from tip to base pull the animal forward. Back ward movement is caused when undulations pass from base to tip. When such undulations are spiral, they cause organism to rotate in opposite direction. 3. Simple conical gyration: Butschlis screw theory postulates a spiral turning of flagellum like a screw. This exerts propelling action pulling the animal forward through water with a spiral rotation as well as gyration (revolving in circles) around the axis of movement. The mechanism producing flagellar beat is not exactly known. It is believed that some or all of axonemal fibers are involved. According to latest sliding tubule, the theory of flagellar (or ciliary) movement, adjacent doublets slide past each other, causing the entire flagellum or cilium to bend. Cross bridges are formed and energy utilized for process is supplied by ATP. iii) Ciliary movement: most ciliates appear to move in a spiral movement is due to in opposite directions on the two sides of pseudopodial filaments together and striking in same direction. Coordination of ciliary movement is due to fact the basal bodies of all cilia are linked by kinetodesmata. Cilia also need liquid medium for their movements Large ciliates are the swiftest swimmers and the champion of them may be named Paramecium caudatum. Ciliary action resembles the swing of a pendulum except that it is more in one direction. Backward and forward vibrations produce a paddle stroke effect.

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Backward effective stroke is more active during which movement is brought about, while forward recovery stroke produces no significant movement. While moving, the succession of beats are coordinated in well- known pattern of metachronal rhythum, conventionally compared to passage of wind over a field of wheat. The evidences strongly suggest that ciliary movement is based on contraction of peripheral fibers. iv) Metabolic movements: This is typical of certain flagellates (eg. Euglena) and most sporozoans at certain stages of their life cycles. Such organisms are seen to show gliding or wriggling or peristalitic movements. Contractile myonemes or microtubules, present in their pellicular walls, are responsible for this type of movement. Movements of this kind are usually also referred to as gregarine movements since they are characteristically exhibited by most gregarines.

Ciliary and flagellar movement

Conversion of sol and gel in amoeba. Large solid arrow indicates direction of movement

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Types of pseudopodia. A. lobopodia of Amoeba, B. filopodia Euglypha, C. reticulopodia of Globigerina , D. axopodia of Actinophrys sol.

END OF PHYLUM RPOTOZOA

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Phylum Porifera General Characters The name Porifera comes from two Latin words (porus: pore; fera: to bear) and constitutes the strange apparently life-less and plant like creatures called sponges. They mark the beginning of cellular (multicellular) animals and are therefore most primitive among them. No distinct tissues or organs.  All Porifera are aquatic, mostly marine except for one family spongillidae which lives in fresh water.  Nutrition is holozoic (type of nutrition involving phagocytosis) and digestion is intracellular.  They are sessile and sedentary and grow like plants. They are solitary or colonial.  Multicellular organisms with cellular grade of body organisation without forming tissues and organs.  Body shape is vase or cylinder like, asymmetrical or radially symmetrical. The size ranges12 micro meter to 1-2 m.  colour also varies greatly, some are grey, bright yellow, red or orange, others have delicate shades of violet or pink, still others are black or white.  Entire body bears pores which are of two types, small but numerous ostia for entry of water currents and large but few oscula for exit of water currents.  Diploblastic animals (two germ layers). The adults body is formed of 2 layers. Outer dermal or pinacoderm of flat pinacocytes and inner gastral layer or choanoderm of flagellated collar cells or choanocytes whose flagella beat and maintain a water current. Between two layers, there is a gelatinous and noncellular mesoglea or mesenchyme.  Almost all sponges possess an endoskeleton. It consists of tiny calcareous or siliceous spicules or of fine sponging fibers, or of both, located in mesenchyme the spicules are secreted by scleroblasts while sponging fibers are secreted by spongioblasts.  Respiration and excretion through general body surface.

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 All cavities in sponge body are intercommunicating whose central cavity is called spongocoel and are collectively referred to as canal system. There are 3 main types of canal system and in order of their increasing complexity are: a) Asconoid, b) Syconoid and c) Leuconoid type.  Sponges do not give visible response to stimuli and only animals without nervous system and sense organs. (presence of neurons arranged in a definite network of bipolar or multipolar cells in some is of doubtful status).  They have higher power of regeneration.  Reproduction takes place both by asexual and sexual methods. Asexual reproduction occurs by budding or by special cell masses, termed gemmules. Sexual reproduction involves formation of ova and sperms. They develop from archaeocytes or choanocytes or both.  All sponges are hermophrodite but cross fertilization is a rule.  Cleavage is holoblastic (type of cleavage in which entire egg is divided) and development is indirect followed by free swimming ciliated larva the amphiblastula or parenchymula. The larva escapes through an osculum with outgoing water currents. There are about 10000 living species of sponges. Their fossils have been reported from rocks of about 600 million years old.

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Canal System in Sponges A distinguishing feature of all sponges is the perforation of body surface by numerous apertures for ingress and egress of water currents. Inside body the water current flows through a certain system of spaces collectively forming the canal system. Most vital role in the physiology of sponges is played by water current on which their life depends. All exchanges between sponge body and external medium are maintained by means of their current. Food and oxygen are brought into body and excreta and reproductive bodies carried out. This current is caused by beating of flagella of collar cells. The arrangement and complexity of internal channels vary considerably in different sponges. Accordingly, the canal system has been divided into 3-types. 1. Ascon 2. Sycon & 3. Leucon. Ascon Type: It is simplest type of canal system which is found in asconoid sponges, like Leucosolenia and in Olynthus stage in the development of all syconoid sponges. Its body surface is pierced by a large number of minute openings called incurrent pores or ostia. These pores are intracellular spaces within tube like cells the porocytes, which extend radially into mesenchyme and open directly into spongocoel. The spongocoel is single, large spacious central cavity in sponge body. It is lined by flagellated collar cells or choanocytes. Spogocoel opens to outside through a narrow circular opening, osculum located at distal free end, and often fringed with large monaxon spicules. Surrounding sea water enters the canal system through ostia. Flow of water is maintained by the beating of flagella of collar cells. Rate of water flow is slow, because the large spongocoel contains much water which cannot be pushed out readily through a single osculum. Course taken by water current in the body of sponge may be shown as under: Unit I

Ingressing of Water Through Ostia Spongocoel Through Osculum To Out Side. Sycon Type: Sycon type of canal system is a more complex system of pores and canals and is characteristic of sycnoid sponges like Scypha (Sycon) and Grantia. It can be theoretically derived from asconoid type of horizontal folding of its walls. Embryonic development of Scypha clearly shows the asconoid pattern converting into sycnoid pattern. Body wall of sycnoid sponges includes two types of canals, incurrent and radial, paralleling and alternating with each other. Both types of canals end blindly in body wall but are interconnected by minute pores. Incurrent pores or dermal ostia, found on the outer surface of body, open into the incurrent canals. These canals are non- flagellated as they are lined by pinacocytes and lead into adjacent radial canals through openings called prosopyles. It is not clear whether prosopyles are channels through porocytes but it is definite that in adult, they are simple intercellular spaces. Radial canals are flagellated chambers as only they are lined by choanocytes. These canals open into central spongocoel by internal ostia or apopyles. Spongocoel is a narrow, non-flagellated cavity lined by pinacocytes. It opens to exterior through an excurrent pore, the osculum, similar to that of ascon type. Course of water current current may be represented as: Ingressing water Dermal Ostia Incurrent Canals Prosopyles Radial Canals Apopyles Spongocoel Osculum to outside. In more complex sycon type, as illustrated by Grantia, the incurrent canals are irregular, branching and anastomosing, forming large sub dermal spaces. This is due to development of cortex, involving pinacoderm and mesenchyme, spreading over the entire outer surface of sponge Leucon Type: As a result of further folding of body wall, the sycon type gives rise to a still more complex canal system, the leucon type. This is characteristic of leuconoid sponges, such as Spongilla. Here radial symmetry is lost and canal system has become very irregular. Flagellated chambers are small, spherical and lined by Unit I choanocytes. All other spaces are lined by pinacocytes. Incurrent canals open into flagellated chambers through prozopyles. Flagellated chambers in their turn communicate with excurrent canals through apopyles. Excurrent canals are developed as a result of shrinkage and division of spongocoel which has disappeared. Thus excurrent canals communicate with outside through an osculum Ingressing of water Dermal ostia Incurrent canals Prosopyles Flagellated Chambers Apopyle Excurrent canals Osculum to outside. Though Leucon type of canal system appears to be the modification of Sycon type, in many calcareous sponges, Leucon type is developed directly without passing through Ascon and Sycon types in their embryology. In Demospongiae, leuconoid condition is derived from a larval stage called rhagon. Spongocoel of rhagon is surrounded by flaggelated chambers opening into it through very wide apopyles. A single osculum opensat the top of spongocoel. Canal system of rhagon larva does not occur in any adult sponge. In demospogiae, leucon type of canal system is also termed the rhagon type because of its derivation from rhagon stage. Leucon type of canal system presents 3-successive grades in its evolutionary pattern. a) Eurypylous type: it is the simplest and most primitive leucon type of canal system. In this type flagellated chambers communicate directly by broad apertures, the apopyles, with excurrent canals. Eg; Geodia. b) Diplodal type: in some sponges, besides aphoda another narrow tube called prosodus, is present between incurrent canal and flagellated chamber. The pattern is called diplodal type, eg; Spongilla, Oscarella.

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Phylum Cnidarian or Coelenterata The word Coelenterate has been derived from two gr. Words, kilos- hollow enteron-intestine as all the animals in this phylum possess a single large cavity the coelentron or gastrovascular cavity. This cavity has only one exist the mouth and performs the functions of digestion and distribution of digested food materials. The coelenterates are regarded as primitive metazoan in which cells are organized to reach tissue grade. General Characters  Phylum Coelenterate also called Cnidarian (gr. Kinida : sting cells) include Polyps, Hydroids, Jelly fishes and Corals.  They are simplest metazoan or first multicellular animals to possess the tissue level of organisation.  All members of this phylum are aquatic, most of them ae marine except hydra which is fresh water, none is parasitic.  They are either colonial or solitary. They are sedentary or free swimming. All are carnivorous.  Symmetry is usually radial. In some forms e.g; sea-anemones have biradial symmetry about a longitudinal oral-aboral axis.  Body encloses a single cavity the coelenteron or gastrovascular cavity which provides the phylum its name. it performs the function of digestion of food and distribution of digested food. This cavity communicates with exterior by a single aperture the mouth there being no anus. The mouth serves for both ingestion of food and egestion of faeces, such digestive cavity is said to be incomplete.  Digestion is partly extracellular that occurs in coelenteron and partly intracellular.  One or both body layers with peculiar stinging cell organelles or nematocysts which serve for adhesion, food capture and offence and defence.  Short and slender tentacles encircle mouth in one or more whorls. These tentacles serve for food capture, its ingestion and for defence.  Body wall diploblastic with two cellular layers- outer epidermis and inner gastrodermis with a gelatinous acellular

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mesoglea in between. In advanced types mesoglea with cells and connective tissue hence triploblastic.  Body organisation of cell-tissue grade. Cells mostly scattered and specialized for different functions. Some cells form tissues like nerve net or nervous tissue.  Exoskeleton chitinous (perisarc) or calcareous(corals).  Body shows two main forms or zooids, the polyp and medusa. The polyp is asexual zooid and is usually cylindrical and fixed, but may be solitary or colonial. The medusa is sexual zooid and is umbrella-like and generally free-swimming, but always solitary. Both forms or zooids have a number of morphological varieties, several of which may exist in a single animal (polymorphism).  When both zooids are founding in same animal the two forms alternate in life-cycle. This phenomenon is termed alternation of generation.  No special organelles for respiration, excretion and circulation. Respiration and excretion occurs through general body surface by diffusion. These are ammonotelic in excretion.  These are acoelomates as there is no separate body cavity or coelom. Muscular system includes longitudinal and circular fibres formed by epithelia-muscle and endothelio muscle cells.  Nervous system is primitive consisting of neurons. The neurons are usually arranged as a nerve net at the base of epidermal and gastrodermal layers. Sense organs may be simple or complex. In some eye spots (ocelli) or statocysts are found, as sensory organs.  Sexes may be separate or united. Reproduction is usually asexual (budding) in polyp form and sexual in medusa form by ova and sperms. Power of regeneration is well marked. In sexual rep. gametes are formed in gonads. Gonads are simple without any duct. Cleavage is holoblastic and sexual forms monoceous or dioecious.  Development indirect with ciliated free swimming sterogastrula, called planula larva. It shows alternation of generation (metagenesis). True alternation of generation is absent.

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Classification of Phylum Coelenterata Phylum Coelenterata includes nearly 11,000 known species half of which are extinct. These are grouped in 3 classes on the basis of development of zooids. I Class Hydrozoan II Class Scyphozoa III Class Anthozoa I Class Hydrozoan: (gr. Hydro: Water, Zoon: Animal) the hydrozoan are commonly called hydroids. They have following characters.  They usually have both polyps and medusa forms and often shows polymorphism and metagenesis.  The polyps have manubrium.  Medusa have true velum.  Mesoglea is noncellular.  Gastrovascular cavity lacks septa (mesentries).  Gonads are ectodermal and shed gametes directly into the surrounding water.  They are chiefly marine, only few being fresh water and usually show radial symmetry. Eg. Hydra, Obelia, Physalia, Vellela. II Class Scyphozoa: (gr. Skyhos: Cup). They are commonly called as jelly fishes.  Medusa form is predominant. It lacks true velum.  Polyp form reduced, but bears a short manubrium.  Mesoglea thick, gelatinous and contains cells.  Gastrovascular cavity lacks mesentries.  Gonads are endodermal and shed the gametes into digestive tract whence they escape through mouth.  Scyphozoa are all marine and solitary form.  They usually show tetramerous symmetry. Eg; Aurelia (jelly fish), Rhizotoma, Pilema, coronata.

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III Class Anthozoa: (gr. Anthos: flower, zoon :animal) they are commonly called sea anemones and corals.  There is only polyp form.  It is without a manubrium.  Mesoglea contains cells and fibres.  Gastrovascular cavity is divided into 8 or more septa or mesentries.  Gonads are endodermal and shed gametes into digestive tract whence escape via mouth.  Symmetry is biradial with hexamerous arrangement of body parts.  They are all marine and mostly fixed. Eg: Adamsia (sea- anemone), Astraea (star coral), Pennatula (sea-pen), Gorgonia (sea fan.)