Protozoology 3rd Year PDF

Protozoology 3rd year Prepared by Dr. Samir A. Taha PROTOZOOLOGY Protozoa are large group of animals which have adapted a cell to serve as the body. The protozoa are not simple in any sense that word; each one...

Protozoology 3rd year Prepared by Dr. Samir A. Taha PROTOZOOLOGY Protozoa are large group of animals which have adapted a cell to serve as the body. The protozoa are not simple in any sense that word; each one is a complete organism performing all the body functions for which a vertebrate animal has many organ systems. Are the protozoa unicellular? A cell is commonly described as a nucleated bit of living material (protoplasm), separated from its environment by a membrane. Most cells have one nucleus. However, many protozoa have more than one nucleus e.g.: Paramecium and other ciliates have one large (macronucleus and one, two or several small micronuclei. Arcella has two identical nuclei. Certain flagellates found in the intestine of insects and the Opalinids in the cloaca of amphibians have many identical nuclei. Some giant free-living amoebas (Pelomexa plustris) have over 100 nuclei, thus protozoa cannot be defined as uninucleate individuals. Is the cytoplasm of protozoa divided into compartments by cell membrane? Usually it is not as in case of the many nuclei of Pelomexa plustris are free in the cytoplasm. On other hand, many protozoa form clustered colonies of many individuals; each with its own membrane and usually a single nucleus. Why do we not consider a colony a single individualand so multicellular organism? The huge colonial algal-protozoan, Volvox globator comes very close to being a multicellular organism, but the cytoplasm of its cells is connected by short tubes which penetrate the cellulose cell walls to form a connected complex of cells (syncytial). Generally, in colonial protozoa, each cell of the colony performs all of its own body functions (i.e. physiologically independent), except perhaps reproductively. 1 Protozoology 3rd year Prepared by Dr. Samir A. Taha Classification of living organisms The following kingdoms of the organisms are: 1. Archetista: are submicroscopic organisms, living in animals, plants or bacteria, in which they cause diseases, e.g. Viruses, Rickettsia. 2. Monera: without nuclei, cell solitary or physiologically independent, e.g. Bacteria, blue green algae, spirochetes. 3. Protista: largely unicellular organisms, with nuclei, e.g. Protozoa, green algae, red algae, brown algae. 4. Fungi: usually organisms with numerous nuclei contain no chlorophyll, usually sessile, e.g. Mashroom, bread mould. 5. Metaphyta or Embryophyta: (Plantae): organisms with chlorophyll, autotrophic, multicellular, usually sessile, e.g. Wheat, corn. 6. Metazoa (Animalia): multicellular organisms, typically holozoic, usually motile, e.g. worms, insects, vertebrate animals. Where to find Protozoa? Protozoa live under almost all natural conditions where moisture is found. They have been described from: 1. Fresh water ponds, lakes, streams: they are clear, cool, spring-fed or warm or stagnant and rich in decaying organic matter. An excellent source is a shallow, semi-permanent pond in a farmyard. The marshes and sloughs on the margins of lakes are as well as any stream large or small temporary or permanent often rich sources. Floating algal mat contain many protozoa. 2. Mud or Sand: there are many mud-dwelling and sand-dwelling species, e.g. Euglena is often found as a green scum on mud flats of rivers. Long ciliates are often found in wet sand or gravel. 3. Moist Soil: in general, these species are not much different from those found in freshwater ponds, but may be different from those found in the ponds. 4. Sewage and Sewage-treatment Plants: species are numerous and differ from those found elsewhere. 5. Marine (Salt) Water: two major groups of protozoa (Foraminifera and Radiolaria) are found only in marine waters. Foraminifera are mostly bottom dwelling forms and live at almost any depth down to 5000 meters, but some are pelagic (floating). Radiolarian species are mostly pelagic but in rough weather they can sink far below the surface. Species of flagellates. Ciliates, 2 Protozoology 3rd year Prepared by Dr. Samir A. Taha amoebas and many groups of Sporozoa can be found in marine water or in marine metazoan animals. Coastal tide pools, attached or floating vegetation, tidal backwater, brackish pool, bays or inlets often have large populations of protozoa. 6. Symbiont Protozoa: may be associated with other organisms which occur either within the protozoan individual or on the outer surface of the cell. The relationship may be commensal, mutualism, parasitic or phoretic. 7. Parasites of Other Organisms: protozoa are known to parasitized : a. Other Protozoa: e.g. Entamoeba that lives in flagellates, Suctorians that live in the cytoplasm of free living ciliates; Sphaerophrya which lives in Paramecium. b. Other Invertebrates: the common parasites of invertebrates are gregarine protozoa that live in the digestive tracts of insects and the seminal vesicle of earth worm. e.g. Monocystis in earth worm; especially in the spring of the year and Grigarina in grasshoppers; especially in late summer and autumn. Many fresh water and marine invertebrates have internal protozoan parasites. c. Vertebrates: some of the most important human diseases are caused by protozoa. e.g. African sleeping-sickness, amoebic dysentery, toxoplasmosis. The amoebas Naegleria and Acanthamoeba affect swimmers by invading the brain through nasal mucosa and the olfactory nerve. Frogs have Trichomonas, Opalina, Nyctotherus and one or more amoebas in the intestine. Guinea pigs are a good source of ciliates; Balantidium. Rats have several flagellates in their intestine and Trypanosoma in their blood. Almost any bird, mammal or reptile may have a species of coccidian’s; e.g. Eimeria in the intestine and malarians in the blood. d. Plants: one flagellate of the genus Phytomonas causes a serious disease of many plants. An amoeba; Labyrinthula and other related genera parasitized several genera of aquatic plants. 3 Protozoology 3rd year Prepared by Dr. Samir A. Taha I. General Characters of Protozoa 1. Protozoa are generally microscopic and acellular animals, they live solitary or in colonial form. 2. The body of Protozoa is naked or covered with a pellicle but in some forms it is enclosed inside a shell and provided with internal skeleton. 3. Protozoa exhibit a great variety of shapes but the spherical, oval and elongated and more or less flattened shapes are most common. 4. The protoplasm of Protozoa is differentiated into an outer clear ectoplasm and inner endoplasm. 5. Nucleus of Protozoa may be vesicular or massive. The vesicular nucleus being spherical, oval or biconvex and contains a central body called endosome (nucleolus) encircle by a zone of nuclear sap. 6. Locomotory organelles being in the form of pseudopodia (as in Sarcodina), cilia (as in ciliates), flagella (as in flagellates). The locomotory organelles may be absent (as in Sporozoa). 7. Respiration in Protozoa takes place through the process of simple diffusion across body surface. 8. Excretion occurs through body surface, but in some species through a temporary opening in the ectoplasm or through a permanent pore called cytopage. The contractile vacuoles serve to remove the soluble waste water. 9. Reproduction may be sexual or asexual. During the life cycle a phenomenon of alternation of generation exhibit (asexual and sexual phases). Also, cysts or protective stages occur during favourable conditions among the fresh and marine Protozoa. 10. All the physiological activities perform by a single cell. 11. Protozoa exhibit two mode of life; free living stages inhabiting fresh, salt water and damp places. Parasitic stages living as an ectoparasites or endoparasites. 4 Protozoology 3rd year Prepared by Dr. Samir A. Taha II. Classification of Protozoa The protozoa are essentially single-celled, eukaryotic organisms. In the classical broad classification of living organisms, which divides them into plants and animals, the protozoa comprise a phylum of animals. At present, over 65000 protozoan species (of which over half are fossils and ~ 10000 are parasitic) have been named. Among living species, about ~ 250 parasitic and 11300 free living sarcodines (of which ~ 4600 are foraminiferans). ~ 1800 parasitic and 5100 free living flagellates. ~5600 parasitic Sporozoa including (Apicomplexa, Microspora, Myxospora and Ascetospora). ~ 2500 parasitic and 4700 free living ciliates. The classical taxonomic scheme of protozoa (1964) was considered Protozoa as a Phylum, divided into 2- subphyla; Plasmodroma (containing the classes: Mastigophora, Sarcodina and Sporozoa) and Ciliophora. This scheme was based primarily on the locomotory organelles. The present classification based on data obtained from the development of the electron microscope where new information becomes available. As in the Society’s 1964 classification, Phyla, Subphyla and Superclasses end in suffix “ea”; Subclasses end in suffix “ -ia”, Orders end in suffix “-ida”, and Suborders end in suffix “-ina”, Superorders not used in Society 1964 but in the present classification “Levine,1980” end in suffix “-idea”. Kingdom: Protista Single type of nucleus, except in heterokaryotic Foraminiferida; A:Phylum: Sarcomastigophora usually reproduce sexually by syngamy, locomotory organelles; flagella, pseudopodia or both. It includes 3- subphyla. I. Subphylum: Mastigophorea Locomotion by flagella 1.Class: Phytomastigophora With chlorophyll, non- parasitic. Order: Cryptomonadida e.g. Cryptomonas sp Order: Dinoflagellida e.g. Ceratium sp Order: Euglenida e.g. Astasia , Euglena Order: Volvocida e.g. Chlamydomonas, Volvox 2.Class: Zoomastigophorea Without chlorophyll, all parasitic. Order: Kinetoplastida e.g. Trypanosoma, Leishmania. Order: Diplomonadida e.g. Giardia Order: Trichomonadida e.g. Trichomonas Order: Hypermastigida e.g. Trichonympha 5 Protozoology 3rd year Prepared by Dr. Samir A. Taha Numerous short flagella, 2- many similar nuclei, all parasitic, II. Subphylum: Opalinata usually in Amphibia. Class: Opalinata With characters of the subphylum. Order: Opalinida e.g. Opalina III.Subphylum: Sarcodina Locomotion mainly by pseudopodia Superclass: Rhizopoda Pseudopodia are not axopods. 1.Class: Lobosea Pseudopodia are lobopods. Order: Amoebida e.g. Amoeba, Entamoeba, Acanthamoeba Order: Schizopyrenida e.g. Naegleria Order: Pelobiontida e.g. Pelomexa Order: Arcellinida e.g. Arceilla, Diffugia 2.Class: Granuloreticulosea Pseudopodia reticulopods. Order: Foraminirida e.g. Textularia, Elphidium 3.Class: Heliozea Pseudopodia are axopods. Order: Actinophryida e.g. Actinophrys, Actinophaerium Trophic stage present, ectoplasmic network present with spindle- shaped or spherical non amoeboid cells. In some genera; amoeboid B: Phylum: Labyrinthomorpha cells move within network by gliding. Saprophytic and parasitic on algae, mostly in marine water. Zoospores produced by most species. Class: Labrynthulea Order: Labrynthulida e.g. Labrynthula sp. Apical complex and microspore present, sexually reproduce by C. Phylum: Apicomplexa syngamy, all species are parasitic. 1.Class: Sporozoea Flagella present in microgametes, heteroxenous. A)Subclass: gregarinia Life cycle; gametogony and sporogony. Order: Eugregarinida e.g. Monocystis sp. b)Subclass: Coccidia Life cycle; merogony, gametogony and sporogony. Order: Eucoccidiida Suborder: Adelina e.g. Haemogregarina sp. Suborder: Eimeriina e.g. Eimeria, Isospora, Sarcocyctis, Toxoplasma. Suborder:Haemosporina e.g. Leucocytozoon, Plasmodium. c)Subclass: Piroplasmia Order: Piroplasmida e.g. Babesia, Theilaria D:Phylum: Microspora Unicellular spores, with one polar filament and one sporoplasm. Spores wall with 3-layers, proteinaceous exposure, chitinous Class: Microsporea endospore and membranous. Order: Microsporida e.g. Nosema 6 Protozoology 3rd year Prepared by Dr. Samir A. Taha Spore multicellular with one or more sporoplasms, without polar E; Phylum: Ascetospora filament, all parasitic. Spore bicellular, consisting of parietal cell and one sporoplasm, Class: Paramyxea spore without orifice. Order: Paramyxida e.g. Paramyxa Spores multicellular, with one or more polar capsules and F: Phylum: Myxozoa sporoplasm, with 1, 2 or 39rarely more) values, all parasitic. Spores with 1 or 2 sporoplasms and 1-6 (typically 2) polar capsules, Class: Myxosporea each capsule with coiled polar filament, coelozoic or Histozoic parasites in cold-blooded vertebrates. Order: Multivolvulida e.g. Hexacapsula sp. Cilia present at some or all stages of life cycle, nuclei of 2- G: Phylum: Ciliophora dissimilar kinds, homothetogenic, sexual reproduction by conjugation. 1.Class:Kinetofragmenophorea Cytostome often apical or subapical or mid-ventral. Cytostomal area superficial apical or subapical, somatic ciliature Subclass: Gymnostomatida usually uniform. Order: Prostomatida e.g. Didymium Vestibulum commonly present apical or near apical (occasionally at Subclass: Vestibuliferia posterior pole), free or parasitic. Order: Trichostomatida e.g. Balantidium Suctotrial tentacles, generally polystomy, widespread on marine Subclass: Suctoria and freshwater organisms. Order: suctoria e.g. Ephelota 2. Class: Oligohymenophorea Oral apparatus partially in buccal cavity. Body ciliature often uniform and heavy, freshwater forms Subclass: Hymenostomatia predominant. Order: Hymenostomatida e.g. Ichthiophthirius, Paramecium Oral ciliary field prominent covering apical end of the body and Subclass: Peritrichida dipping into infundibulum. Order: Peritrichida e.g. Vorticella Somatic ciliature complete or reduced or appearing as cirri, 3. Class: Polymenophorea cytostome at bottom of buccal cavity or infundibulum. Subclass: Spirotrichia With characters of the class. Order: Heterotricida e.g. Blepharisma, Spirostomum, Stentor, Nyctotherus Order: Hypotrichida e.g. Kerona, Euplotes, Stylonchia 7 Protozoology 3rd year Prepared by Dr. Samir A. Taha NOTES IN PROTOZOA 1. Nucleus and Cytoplasm in Protozoa Together with metazoa and most plants protozoa are described as eukaryotes; their genetic materials (DNA) is carried on well defined chromosomes combined with a protein (histone) and the chromosomes are contained within a membrane-bounded nucleus. Like all cell, the bodies of protozoa are covered by a trilaminar unit membrane. The membrane appears three layered in electron micrographs because the central lipid portion appears light or clear (electron lucent) and is surrounded by the darker portion (electron dense). As in other eukaryotes, the nuclei of protozoa are bounded by a double unite membrane with pores. Several other membranous organelles are represented; endoplasmic reticulum, mitochondria, Golgi apparatus and so on. The cytoplasmic matrix consists of very small granules and filaments suspended in a low density medium with the physical properties of colloid. Central and peripheral zones of cytoplasm distinguished as the endoplasm and the ectoplasm. The endoplasm is in the sol state of colloid and bears the nucleus, mitochondria, Golgi bodies and so on. The ectoplasm is in gel state of colloid and appears more transparent under the light microscope and helps to give rigidity to the protozoan body. The base of the flagella and cilia and their associated fibrillar structures are embedded in the ectoplasm. The outermost membrane is called pellicle. Nuclei of protozoa exhibit a wide variety of appearance, particularly under the light microscope. The most common type of nucleus in protozoa other than ciliates is described as vesicular. The nuclei are characterized by such an irregular distribution of chromatin material (peripheral or internal) that appears as clear areas in nuclear sap. Generally on or more nuclei may be present. Endosomes, conspicuous internal bodies, are thought to be analogous to nucleoli in metazoan animals. For example; amoebas, trypanosomes and phytophlagellates have endosome. The types of nuclei in protozoa are: 1. Vesicular nucleus Have a large amount of nucleoplasm, small amount of chromatin that forms small and coarse granules, the achromatin (oxychromatin) is more fluid and forms network, if present. The endosome consists of basi-or oxy-chromatine. e.g. Euglena, Arcella. 8 Protozoology 3rd year Prepared by Dr. Samir A. Taha 2. Massive nucleus Have a small amount of nucleoplasm, large amount of chromatin that forming scattered small granules achromatin (oxychromatin) is viscid forming a fine net-work. e.g. Amoeba. In the majority of protozoa the nuclei show a structure intermediate between the vesicular and massive nuclei. 3. Polyenergid nucleus Have several sets of chromosomes, instead of one set, inside the nuclear membrane. Finally, a set of chromosomes librated and forms a new nucleus. The polyenergid nucleus is a provision for spore formation. e.g. Radiolaria. 4. Dimorphic nucleus Found in Ciliates, the large one is macronucleus; containing trophochromatin_ controls the vegetative functions, divides amitotically, disappears during conjugation and replaced by material from synkaryon. The shape of the macronucleus is much varied (band shaped, moniliform or branched). The second nucleus is small and round micronucleus; may be one or more micronuclei_ contain idiochromatin, controls reproduction, divides mitotocally in binary fission and conjugation and gives rise to macronucleus when the latter disintegrates. Usually protozoa have a single nucleus, but many have more than one. When the nuclei are more than one, they may be alike. For example in Sarcodina may have many similar nuclei, as in Arcella and hundreds as in Pelomyxa.In Trypanosoma there are two dissimilar nuclei; the principal one is the trophonucleus –regulates metabolism- and being of vesicular type. While the second one is kinetonucleus- controls the locomotory organelles and being of massive type. 9 Protozoology 3rd year Prepared by Dr. Samir A. Taha 2. Nutrition in Protozoa The process by which the organisms derive their nourishment, digest and assimilate the food is called Nutrition. However, protozoa obtain nourishment in various ways: 1. Autotrophic or Holophytic Nutrition: Protozoa with chlorophyll or some allied pigments can manufacture complex organic food from simple inorganic substances, e.g. Euglena, Noctiluca. Often there may be protein bodies called Pyrenoids which represent the center of photosynthesis. Some protozoa have no chromatophores but have chlorophyll-bearing algae Zooxanthellae and Zoochloryllae (as represented in marine and freshwater respectively). Such animals manufacture their organic food for the host by the process of photosynthesis as represented in Stentor, Thalassicola. Nitrates or ammonium compounds are sufficient as a source of nitrogen for autotrophic forms. 2. Holozoic or Zootrophic Nutrition: Some protozoa require ready-made proteins as food, because they are unable to utilize the simple substances for making their own food. Such protozoa are called Zootrophic organisms like Amoeba. Complex organic food is swallowed at a temporary opening or a permanent mouth where the food is enclosed in food vacuoles. Food vacuoles circulate in the endoplasm by streaming movements (as in Amoeba) or by peristalsis movement (as in (Vorticella). Undigested food materials cast off at any point if there is no pellicle (as in Amoeba) or through a temporary or permanent cytoproct in species hven’t pellicle (Paramecium) 3. Saprozoic Nutrition: Some protozoa absorb complex organic substances in solution through the body surface, they called saprozoic organisms. Saprozoic forms need ammonium salts or peptones for their nutritional requirements. Decaying animals and plants in water form protein and carbohydrates. The saprozoic protozoa may be free-living (as in Euglena) or parasitic (as in Monocystis). Some parasitic protozoa can also ingest solid food (as in Balantidium). 4. Mexotrophic Nutrition: Some protozoa feed themselves by more than one method at the same time or at different times due to change in the environment, referred to mixotrophic nutrition. For example Euglena is both saprozoic and autotrophic, some green flagellates are both 10 Protozoology 3rd year Prepared by Dr. Samir A. Taha autotrophic and Zootrophic, while Paranema saprozoic and holozoic nutrition is represented. Generally protozoa which feed on a large variety of food organisms are called Euryphagous and those feed on a few kinds of food are called Stenophagous. On the basis of the nature of food and feeding mechanism, protozoa are placed in the following groups: 1. Microphagous Feeders: Protozoa which feed on very small particles, they rarely stop feeding and their food is drawn in with a current of water (as in Paramecium). 2. Macrophagous Feeders: Protozoa which feed on large pieces of food particles (as in Amoeba). 3. Fluid Feeders: Protozoa which feed both saprozoic and parasitic, where they absorb their own fluid food through their body surface (as in Monocystis). Digestion in protozoa is intracellular within food vacuoles. The food vacuoles undergo changes in pH and in their size during digestion. At first the contents of the food vacuoles are acidic and the vacuoles decrease in size, during this phase living prey dies. After the initial acid phase, the cytoplasm produced enzymes which pass into the food vacuoles, thus increase in size and become alkaline. Finally, the contents of the food vacuoles digested and the undigested materials remain to egest exterior. 11 Protozoology 3rd year Prepared by Dr. Samir A. Taha 3. Excretion and Osmoregulation in Protozoa Most protozoa appear to be ammonotelic, that is, they excrete most of their nitro- genous materials as ammonia, where most of which readily diffuse directly through the body membrane into the surrounding medium. Others, sometimes, produced unidentified waste products (as in intracellular parasites). These substances are secreted and accumulated within the host cell and on its death produce toxicity to the host. However, carbon dioxide, lactate, pyruvate are also common waste products. Contractile vacuoles are probably more involved with Osmoregulation than with Excretion. Because the free-living freshwater protozoa are hypertonic to their environment, they imbibe water continuously by osmosis. The action of contractile vacuoles effectively pumps out the water. Marine protozoa and most parasites don’t form these vacuoles, probably, because they are isotonic to their environment. However, trypanosomes and Balantidium organisms contain contractile vacuoles. 12 Protozoology 3rd year Prepared by Dr. Samir A. Taha 4. Locomotion In Protozoa Locomotion is the movement or progression through the medium in which the animals change their place and position so as to get its food material. Protozoa move about by means of pseudopodia, flagella, and cilia. The seat of locomotion lies in the ectoplasm, since locomotor organelles either arise from or are parent in it. Types of locomotory organelles in Protozoa: 1. Pseudopodia Pseudopodia are generally temporary outgrowths of protoplasm from any part of the body, they are found in those protozoa which are naked or have a very thin pellicle. Pseudopodia may be of ectoplasm or they may also have a core of endoplasm. The following kinds of pseudopodia are met with: a. Lobopodia Are blunt, short or finger-like, they are made of ectoplasm with a core of fluid endoplasm, for example; Arcella, Amoeba. b. Filopodia Are fine, long threads, often with rounded ends, at times they may branched. They made of only hyaline ectoplasm, for example; Radiolaria. c. Rhizopodia or Reticulopodia Are thin, long and branched. The branches of adjacent pseudopodia may anastomose to form a network which also serves as a trap for capturing food , for example; Elphidium d. Axopodia Are long, stiff threads made of ectoplasm, with a hard central axial filament, unlike others, they are semi-permanent and not only organelles of locomotion but for capturing food, for example; Actinophrys. 2. Flagella Flagella are extremely fine fibrils having a central axoneme made of two longitudinal fibrils and an enveloping protoplasm sheath having nine double longitudinal fibrils that forming a ring. All 20 fibrils lie in a matrix of dense cytoplasm and they fuse at the base to join a basal granule (kinetosome). The kinetosome may be joined to the nucleus by a rhizoplast. The basal granule is often synonyms with a centriole because it initiates nuclear divisions- if it does not act as a centriole- then it is connected by a rhizoplast to a centriole or to the nucleus. There are different kinds of the flagella, at the tip of the main flagellum may be a very fine end piece or mastigoneme, or the main axis of the flagellum may bears fine flexible lateral processes or mastigonemes on one side or both 13 Protozoology 3rd year Prepared by Dr. Samir A. Taha sides. Mastigonemes constitute the so–called flimmer or ciliary flagellum. Flagella perform lashing movements with a rowing action or undulating motion. In rowing action the flagellum is held rigid but slightly concave in the direction of the stroke. In recovery stroke flagellum bends obliquely and undulations pass along the flagellum from the base to the tip causing the animal to rotate around its axis. Some species may contain one flagellum that emerges from the opening at the anterior end, for example; Astasia or there may be two equal flagella, for example; Chlamydomonas, or there may be two flagella, one short and the other thick and long, for example; Noctiluca. Some species may have many flagella, for example; Opalina. Generally most flagellates don’t have more than our four flagella. Flagella are primarily organelles of locomotion and secondarily for capturing food. 3. Cilia Cilia are exactly like flagella in structure and there is no real distinction between them, except in the methods of working. The primitive forms cilia cover the entire body, but in more specialized forms cilia are restricted to certain regions only. Cilia arise from kinetosomes, from each kinetosome arises a rhizoplast which does not join the nucleus, nor do cilia bear any mastigonemes. Running slightly to the right of longitudinal row of kinetosomes is a delicate thread called kinetodesma. A row of kinetosomes with its kinetodesmata forms a longitudinal unit called kinety. All kinetia of an animal constitute its Infraciliary system. Infraciliary system is characteristic of all ciliates, even in those forms in which cilia are lost in the adults, where the Infraciliary system is retained. Cilia are arranged in straight or spiral twist, then straightening out; where their beating is in a metachromal rhythm. Movements of cilia bring about locomotion in a liquid medium, and the currents they produced are used for obtaining food. The Infraciliary system of ciliates differs from that of flagellates in the following respects: a. The cilia are generally shorter and more numerous than flagella. b. In ciliates the infraciliature is not joined to the nucleus i-e kinetia are not inter- connected. In flagellates rhizoplasts join the kinetosomes to the nucleus, and the kinetia may be inter-connected. c. In cell division of ciliates the cleavage is perkinetal because it cuts across all kinetia, where the upper halves go to one daughter cell and the lower halves go to the other daughter. This type of division is called homothetogenic; in which the daughter cells are duplicated of each other. In a cell division of 14 Protozoology 3rd year Prepared by Dr. Samir A. Taha flagellates, the cleavage is interkinetal because it is longitudinal and parallel to kinetia, so that kinetia are not cut but are shared by daughter cells. This type of division is called symmetrogenic; in which the daughter cells are duplicated but mirror of each other. [The normal number of kinetia are restored by division of kinetosomes] d. Cilia have no mastigonemes as in flagella. The cilia may be forming the following composite motile organelles: i. Membranelles Are membranes formed by fusion of two or more adjacent transverse rows of short cilia. They are found in the peristome making powerful sweeps of food, for example Paramecium. ii. Undulating membranes Are made of one or more longitudinal rows of cilia fusing together. They are found in peristome and cytopharynx and used to collect food, for example Vorticella. The undulating membrane of Trypanosoma is only a web of ectoplasm i-e not made of cilia and it is locomotory function. iii. Cirri They are formed by fusion of two or three rows of cilia on the ventral side of some ciliates. They are locomotory and may be tactile functions, , for example Stylonchia. iv. Myonemes They are contractile fibrils in the ectoplasm, surrounded by a canal and may form a network. Myonemes have alternate rows of light and dark substances, for example Stentor. Myonemes are found in flagellates, ciliates and sporozoans. They are primarily organelles for metaboly (wave of contractions and expansions, for example Paramecium), and secondarily for locomotion by muscle-like contraction, for example Monocystis. 15 Protozoology 3rd year Prepared by Dr. Samir A. Taha 4. Reproduction In Protozoa The process of reproduction is to continue one’s kind in nature. The mode of reproduction in protozoa is slightly variable among different groups although it is primarily a cell division. Protozoa reproduce both asexually and sexually. I. Asexual Reproduction In asexual mode of reproduction there is always some form of fission present. An essential part of the process is partition of some parent chromatin substance among daughter individuals. Hence, the fission of the cell body is preceded by the division of the nucleus. Asexual reproduction occurs by the following methods: 1. Equal or Binary fission Equal or binary fission takes place for reproducing and also for gamete formation. Usually there is a centriole within the nucleus, but unlike metazoa no asters are formed. Moreover, the nuclear membrane persists intact during division in most protozoa. The nucleus elongates and divides amitotocally into two parts which travel apart, finally the cell contracts at the middle to form two daughter cells (macronucleus in ciliates). Binary fission is usually transverse; in which both the nucleus and cell divide tansies, but in most flagellates it is longitudinal; in which nucleus elongates transversely but the cell divides lengthwise. In binary fission a single flagellum is retained usually by one daughter cell and the basal granule divides into two parts, where the new basal granule forms a flagellum in the other daughter cell. When there are many flagella; they are distributed among the daughter cells which grow new flagella to complete the number. Cilia are shared by daughter cells and new cilia are formed by kinetosomes to complete the number. Chromatophores usually divide but contractile vacuole rarely divides; they are generally shared or are made a new one. Complex organelles are destroyed and then renewed in the daughter cells. 2. Multiple Fission The nucleus divides repeatedly without division of the cytoplasm, later the cytoplasm separates into as many parts as there are nuclei, and usually some residual cytoplasm is left unsegmented. If multiple fission produces four or more young ones by equal cell division and the young ones do not separate till the process is completed, then such cell division is called repeated fission, for example Vorticella. Multiple fissions produce small cells which may grow into adults or may become gametes which require fertilization before development. Multiple fission may lead 16 Protozoology 3rd year Prepared by Dr. Samir A. Taha either to asexual or sexual reproduction, For example in Plasmodium multiple fission occurs after fertilization to form sporozoites. Products of multiple fission of a zygote generally form Spores. A spore may be enclosed in a spore case (Monocystis) or may be naked. The naked spores may be amoeboid (Entamoeba) or flagellated (Chlamydomonas) or ciliated (Suctoria). Spores may be gametes or serve for the distribution of species. All types of fission occur within or without encystment. Cyst formation is common in freshwater and parasitic protozoa. During cyst formation, the animal becomes rounded, loses its organelles of locomotion, ejects its food vacuoles and contractile vacuoles disappear. The animal secretes a gelatinous covering which hardens into a chitinous epicyst; inside this a membranous endocyst is secreted. The cyst may have more than two layers. The function of the cyst is protection the animal against unfavourable conditions of the environment, or it may be for reproduction. The cyst can be carried by wind or some other agents, so it is important in dispersal of the species. Protozoa have the following kinds of cysts: a. Resting cysts: enable the animal to proceed undisturbed in its normal activities, Euglena. b. Resistance cysts: are formed against unfavourable conditions of environment, Amoeba. c. Gametocysts: in which gametes union together for reproduction, Gregarina. d. Oocysts: contain a zygote, Plasmodium. e. Sporocysts: are those in which multiple fissions occur to form sporozoites, Monocystis. Finally excystment takes place on return of favourable conditions, but the individual leaving the cyst is never the same as the one that underwent encystment, it has a complement of a new organelles and renewed vigour. The excystment may be through a minute pore in the cyst, but in more cases it is usually due to some enzymes secreted by the protozoan individuals. 3. Plasmotomy An asexual division of a multinucleate animal, in which the cytoplasm divides but the nuclei do not so, (Opalina, Pelomexa). Later, each daughter cell regains the number of nuclei by nuclear division. The plane of division may be monotomy (Opalina) or syntomy (Pelomexa). 17 Protozoology 3rd year Prepared by Dr. Samir A. Taha 4. Budding or Gemmation An unequal division of the parent body produces one or more buds which may separate from the parent; the nucleus of the buds is a part of the parent nucleus, e.g Arcella. The bud is smaller than the parent and may grow into adults or may become gametes. When the buds are formed on the surface of the parent, they called Exogenous Budding e.g. Noctiluca; which produce hundreds of buds on its surface as small protuberances. When the buds are formed inside the cytoplasm and remain within the parent, then the process is called Endogenous budding, e.g. Arcella becomes multinucleate and the protoplasm collects around the nuclei to form many amoebulae which escape from the parent and grow into adults. 5. Parthenogenesis It the ability of the gametes to develop into adults without fertilization by gametes of the opposite sex, the gamete possessing this power is almost the female one, e.g. in Actinophrys; 2-individuals get enclosed in a cyst, each divides to form 2-gametes, one gamete of an individual conjugates with a gamete of the other individual, the remaining gamete of each individual develops parthenogenically into an adult. Endomixis of ciliates is also a parthenogenetic phenomenon. The chromosome condition in parthenogenesis may be expected to be haploid since no fertilization occurs, but it is generally diploid. 6. Regeneration Regeneration is the capacity to form new tissue to replace a lost part; this capacity varies inversely with the complexity of an organism. In protozoa any nucleated portion is capable of regeneration, while non-nucleated portions are not; e.g. Stentor has a long chain-like nucleus, If the animal is cut transverselly into say 3-parts, then each piece having a portion of the nucleus will regenerate the missing portions and 3-Stentors will be formed. 7. Endodyogeny This type is found in Toxoplasma, where 2-daughter individuals developed within the parent cell nucleus which is then destroyed. The process looks-like interbudding or special type of multiple fissions. II. Sexual Reproduction 8. Skeleton In Protozoa 9. Economic Importance of Protozoa 18 Protozoology 3rd year Prepared by Dr. Samir A. Taha 10. Protozoa and Disease 11. Behaviour in Protozoa 19