Protista: Unicellular Eukaryotes PDF

Unicellular Eukaryotes: The Protista DOMAIN OF LIFE  The first evidence for life on earth dates from approximately 3.5 billion years ago and were prokaryotes (Bacteria and Archaea) whose descendants diversified greatly over an enormous time span. The common ancestor of eukaryotes...

Unicellular Eukaryotes: The Protista DOMAIN OF LIFE  The first evidence for life on earth dates from approximately 3.5 billion years ago and were prokaryotes (Bacteria and Archaea) whose descendants diversified greatly over an enormous time span. The common ancestor of eukaryotes was formed by merging cells through symbiogenesis  Mitochondrion capable of deriving energy from carbon compounds using oxygen originated from engulfed alpha- proteobacterium through primary endosymbiosis. While plastids capable of photosynthesis originated from an engulfed cyanobacterium  Eukaryotes are organisms with nucleus and other membrane enclosed organelles such as mitochondria and Golgi apparatus. Eukaryotic cells also have a well developed cytoskeleton that provides the structural support that enables them to have asymmetric (irregular) forms as well as change shape when they feed, move and grow.  Unicellular eukaryotes is a complete organism in which all life’s activities occur within the limits of a single plasma membrane The most numerous and diverse eukaryotes are the protists which are mostly single-celled organisms. Any eukaryote that is not a fungus, plant or animal is classified as Protista  With few exceptions, modern eukaryotic cells possess the energy-producing organelles termed mitochondria, and photosynthetic eukaryotic cells possess chloroplasts, the energy harvesting organelles. Mitochondria and chloroplasts are both believed to have entered early eukaryotic cells by a process called endosymbiosis Diversity of protists stems from endosymbiosis. Mitochondria descended from proteobacteria, a purple sulfur bacteria and a relatives of parasitic Rickettsia that were incorporated into eukaryotic cells early in the history of the group  While Chloroplasts are derived from cyanobacteria The large number of eukaryotes that do not fit into any of the three eukaryotic kingdoms are arbitrarily grouped into a single kingdom called Protista Some protist are more closely related to plants, fungi or animals than they are to other protist  FEATURES OF PROTISTA Eukaryotic; presence of nucleus and membrane-bound organelles. Mostly single celled or exist as group of similar cells. Some have animal-like cells (no cell wall) wrongly grouped together as phylum protozoa. Others have plant-like cells (with cellulose cell walls and chloroplasts)  Unicellular protists carry out essential life function using subcellular organelles. Certain protists rely on organelles not found in most other eukaryotes, eg the contractile vacuoles that pump excess water from the cell. Ocelloid with component resembling lens and retina is an eye-like organelle in the dinoflagellates  Often, they are more complex than any particular cell in higher organisms. Some protists form colonies yet independent on one another for most functions. Some colonies can become complex, yet their level of organization is at protoplasmic grade.  Assemblage of eukaryotic unicellular organisms was initially called protozoa. Protists represent all symmetries and exhibit all types of nutrition Some protists are plantlike because they are primarily autotrophic Others are animal-like because they are primarily heterotrophic Yet others combine autotrophy and heterotrophy in a new mode called mixotrophy  Heterotrophic may involve ingesting food in a soluble form (osmotrophs or saprozoic) or in a particulate form (phagotrophs or holozoic feeders). Autotrophic protists are either photosynthetic or chemoautotrophic In a typical protist regular arrangement of microtubules, called the pellicle, underlies the plasma membrane of many protista. The pellicle is rigid enough to maintain the shape of the cell, but it is also flexible cytostome A PROTIST  The Cytoplasm is not homogeneous; sometimes peripheral and central areas can be distinguished as: Ectoplasm is more transparent (hyaline) by light microscopy, and it bears the bases of the cilia or flagella Endoplasm appears more granular and contains the nucleus and cytoplasmic organelles  Water enters freshwater cells with higher solute concentrations by osmosis. Contractile vacuoles remove this excess water Some protists ingest food through a specialized region cytostome and cytopharynx, analogous to a mouth. Phagotrophic heterotrophs ingest visible particles of food by pulling them into intracellular vesicles called food vacuoles or phagosomes  Lysosomes fuse with food vacuoles that form during endocytosis to introduce enzymes that digest the food particles. After digestion is complete, the egestion vacuoles release their waste contents by exocytosis at a specialized region of the plasma membrane or pellicle called the cytopyge.  REPRODUCTION Protista reproduce both sexually and asexually One of the simplest and most common forms of asexual reproduction is binary fission. Here the nuclear membrane persist throughout mitosis with the microtubular spindle forming within it  Longitudinal binary fission in euglenoids Longitudinal binary fission in the Euglena begins with mitosis and then cytoplasmic division (cytokinesis) divides the organelles b/w the two cells and results in two similarly sized organism. Nuclear envelope remain intact during mitosis Transverse binary fission in ciliates  Budding is another form of asexual reproduction in which mitosis is followed by the incorporation of one nucleus into a cytoplasmic mass that is much smaller than the parent cell. In Schizogony or multiple fission cell division preceded by several nuclear division This allows cytokinesis to produce several daughter cells almost simultaneously.  Most eukaryotes undergo Sexual reproduction. Meosis allows for the production of haploid cells, the gametes, and the subsequent fusion of gametes to form a zygote. In some protists, the sexually mature individual is haploid. Gametes in these case are produced by mitosis, and meiosis follows the union of the gametes.  LOCOMOTION Several means of locomotion: Some wave one or more flagella to propel them through water Others use banks of short flagella-like structure called cilia to create water current for movement and feeding, Pseudopods are the chief means of locomotion among the amoebas Yet in other protists move by means of undulating their plasma membrane.  Eukaryotic flagella are extensions of the cytoplasm, consisting of bundles of microtubules covered by the cell’s plasma membrane. They are quite different from prokaryotic flagella, which are filaments composed of globular proteins attached to the cell surface. There is no real morphological distinction between cilia and flagella Means of locomotion used in old classifications Originally, the means of locomotion was used to distinguish unicellular eukaryotes: Flagellates use flagella Ciliates travel via a ciliated body surface Amebas extend their pseudopodia to move Protists constitute such an unnatural group and therefore using locomotory structures leads to chaotic grouping of genetically unrelated organisms. A cross section through a Flagellum  Outward extension of the cytoskeleton and cytoplasm forms the pseudopodia used for movement and feeding in Amoebas Lobopodia are blunt and broad cell processes containing ectoplasm and endoplasm  Filopodia are thread-like and contain ectoplasm only Reticulopodia are net-like series of cell extensions Axopodia are thin filamentous cell extension supported by a central axis of microtubules  Recent classification using metagenomic studies grouped the protists according to their phylogenetic relatedness. Microsporidians once considered amitochondriate protists are now classified as fungi Comparison of the features of the six kingdoms Eukaryotic evolutionary relationships  Supergroup EXCAVATA The Diplomonads, Parabasalids and Euglenozoans are genetically related and grouped under a supergroup EXCAVATA based cytostkeletal and DNA sequence , and the presence of excavated feeding groove on one side of the cell body Excavata has a posteriorly directed flagellum which generate feeding current  Two major clades (the parabasalids and diplomonads) have two nuclei, multiple flagella and modified mitochondria; Members of the third clade (the euglenozoans) have flagella that differ in structure from those of other organisms and several have acquired chloroplasts through endosymbiosis. Excavates include parasites as well as many predatory and photosynthetic species.  Diplomonads Giardia intestinalis placed under Diplomonads based on modified mitochondria called mitosomes Mitosomes lack functional electron transport chains and hence get the energy they need from anaerobic pathway  Other features include possession of multiple posterior flagella and two haploid nuclei per cell. G. intestinalis lacks the characteristic surface groove of the Excavata and inhabits the intestines of mammals. It can infect people when they drink water contaminated with feces containing Giardia cysts which can cause severe diarrhea. Boiling the water kills the parasite. Giardia intestinalis  Parabasalids Distinguishing feature is the possession of undulating membrane used in locomotion in addition to flagella also used in propelling themselves. They have one nucleus per cell and reduced mitochondria called hydrogenosome that generate energy anaerobically releasing hydrogen gas. Some live symbiotically in guts of termites and cockroaches where they digest cellulose in their wood-based diet.  The best-known parabasalid is Trichomonas vaginalis, a sexually transmitted trichomoniasis that infects about 140 million people each year worldwide. T. vaginalis travels along the mucus coated lining of the human reproductive and urinary tracts by moving its flagella and by undulating part of its plasma membrane. In females, if the vagina’s normal acidity is disturbed, T. vaginalis can outcompete beneficial microorganisms there and infect the vagina. Trichomonas vaginalis  Euglenozoa Euglenozoans belong to a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, mixotrophs, and parasites illustrating the impossibility of distinguishing plant-like and animal-like protists. The main morphological feature that distinguishes Euglenozoa is the presence of a rod with either a spiral or a crystalline structure inside each of their flagella. Their body shape change while swimming alternating b/w being stretched out and rounded up  Two monophyletic subphyla Euglenida and Kinetoplasta Euglenida: has a pocket/reservior at one end of the cell from which one or two flagella emerge One third have chloroplast and autotrophic others lack chloroplast and are hertertrophic Some euglenids are mixotrophs: They perform photosynthesis when sunlight is available, and become heterotrophic absorbing organic nutrients from their environment in absence of sunlight. Many other euglenids engulf prey by phagocytosis Euglena viridis  Kinetoplasta Kinetoplastids have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast. These protists include species that feed on prokaryotes in freshwater, marine, and moist terrestrial ecosystems, as well as species that parasitize animals, plants, and other protists. Eg, Trypanosoma brucei that infect humans and cause sleeping sickness  This neurological disease currently afflicts about 10,000 people each year, mostly in rural areas of Africa. Where the infection occurs through the bite of a vector tsetse fly (Glossina spp.). Trypanosoma cruzi is another trypanosome that causes American trypanosmiasis or Chagas’ disease in humans in Central America and South America. It is transmitted by “kissing bugs” (Triatominae) Acute Chagas’ disease is most commonly severe among children less than five years old.  Two to 3 million people in South and Central America show chronic Chagas’ disease, and 45,000 of these die each year. Other parasitic Kinetoplastids include several species of Leishmania cause different types of leishmaniasis in humans. Leishmaniasis are transmitted by sand flies (Phlebotomus and Luzomyia) in Africa and Asia, and Central America and South America. SUPERGROUP CHROMALVEOLATA  The stramenopiles and alveolates form a monophyletic supergroup based on whole- genome DNA sequence analyses. It was suggested that stramenopiles and alveolates, originated when a common ancestor of these two clades engulfed a single-celled, photosynthetic red alga. Because red algae are thought to have originated by primary endosymbiosis such an origin for the stramenopiles and alveolates is referred to as secondary endosymbiosis.  ALVEOLATA Members of this subgroup have membrane- bound sacs (alveoli) beneath the plasma membrane In the Ciliophora, the alveoli produce pellicles; In the Dinoflagellata, the alveoli produce thecal plates; In the Apicomplexa, the alveoli have structural functions  DINOFLAGELLATA Approximately half of the dinoflagellates species are photoautotrophic. The rest are colorless and heterotrophic Ancestral dinoflagellates probably were heterotrophic, and some acquired chloroplasts through secondary endosymbiosis from algal sources Many are mixotrophic  FEATURES: They commonly have two flagella, one equatorial and one longitudinal, each borne at least partially in grooves called the sulcus which it uses for spinning through water. The body may be naked or covered by cellulose plates or valves Ceratium for example, has a thick covering with long spines, into which the body extends  Many of the living species of photosynthetic dinoflagellates are also heterotrophic to some extent, and some with functional chloroplasts can switch entirely to heterotrophy in the absence of sufficient light some species are among the most important primary producers in marine environments The feeding mechanisms of heterotrophic dinoflagellates are quite diverse while some heterotrophs feed by saprotrophy, other dinoflagellates ingest food particles by phagocytosis.  Many species can ingest prey through a permanent cell mouth between the plates near the posterior area of the body The cytostome is supported by sheets of microtubules Ceratium can catch food with posterior pseudopodia and ingest it between the flexible plates in the posterior groove.  Many, in fact, are voracious predators that ingest other protists and microinvertebrates or use specialized cellular appendages to pierce prey and suck out their cytoplasmic contents. Noctiluca, a colorless dinoflagellate, is a voracious predator and has a long, motile tentacle, near the base of which its single, short flagellum emerges. Noctiluca is one of many marine organisms that can produce light (bioluminescence).  Parasitic dinoflagellates have a broad range of hosts, morphological diversity, and life histories. The genus Haplozoon is a small group of intestinal parasites occurring in marine worms. Haplozoon have long been viewed as "multicellular" or "colonial“ in their organization. However, recent studies revealed a unique cellular organization in which the entire organism is bounded by a single continuous membrane, suggesting syncytial composition of cell-like compartments separated by sheets of alveoli.  Dinoflagellate bloom called red tide make coastal waters brownish red or pink The colour is as a result of carotenoids in the pastids However, any instance of a bloom producing detectable levels of toxic substances is now called a red tide Dinoflagellates such Gymnodinium produce toxin that can cause massive fish kill Consuption of tainted mollusc or fish affects humans sometimes fatally  The water may be red, brown, yellow, or not remarkably colored at all. The toxins do not harm the dinoflagellates, but if they are present in high concentrations they can harm fish or other marine life. In area where clams, mussels, oysters or other filter-feeders are harvested for human consumption, the beach will be closed during a red tide. Closure will last until the filter-feeders have digested all the dinoflagellate toxin that they consumed Red Tide  CILIOPHORA FEATURES Cilia often cover the entire cell or may be clustered in a few rows or tufts Some ciliates lack cilia as adults, although cilia occur at other stages in the life cycle Cilia used for swimming and feeding arise from subsurface basal granules Cilia are identical to flagella. Major difference is in the number  Cilia may cover the surface of the organism or may be restricted to the oral region or to certain bands. In some forms cilia are fused into a sheet called an undulating membrane or into smaller membranelles, both used to propel food into the cytopharynx Cilia may be fused forming stiffened tufts called cirri, often used in locomotion by the creeping ciliates  Possess two type of nuclei: micro and macronucleus A cell has one or more of nuclei of each type Possesses Large contractile vacuole Complex organelles mostly as part of the pellicle  Shape maintained by the complex pellicle Ciliates possess distinct anterior Food is ingested through the cytostome and cytopharynx Food digestion occurs within the food vacuole Contractile vacuoles provide for water balance Paramecium a Ciliophoran  Micronuclei is for exchange of genetic information during conjugation Macronuclei is required for producing RNAs and Proteins for daily functions During asexual reproduction by binary fission macronucleus divide into two pieces and new gullet and two new contractile vacuoles appear BINARY FISSION IN CILIOPHORA  Conjugation is the temporary union of two individuals to exchange chromosomal material During conjugation the haploid micronuclei resulting from meiotic division function as gametes During the union the macronucleus disintegrates and the micronucleus of each individual undergoes meiosis, giving rise to four haploid micronuclei, three of which degenerate CONJUGATION IN CILIOPHORA  The remaining micronucleus then divides into two haploid pronuclei, one of which is exchanged with the other conjugant. The pronuclei fuse to restore the diploid number of chromosomes Sexual reproduction permits gene recombinations, thus increasing genetic variation in the population Thus the exconjugants contains hereditary material from two individuals.  Most ciliates are free-living in freshwater or marine habitats, but commensal and parasitic forms do occur The free-living Ciliates may be predatory or suspension feeders while symbiotic may be commensal and parasitic and live within the vertebrate gut. Balantidium coli is a common parasite of man, lower primates and hogs  Usually the organisms are not pathogenic, but in humans they sometimes invade the intestinal lining. Infections result from fecal contamination of food Pathogenesis is similar to that of E. histolitica. Ichthyophthirus multifillis is a ciliate fish parasite APICOMPLEXA  Almost all apicomplexans are endoparasitic Lack visible means of locomotion although Pseudopodia occur in some intracellular stages, and gametes of some species are flagellated. The presence of a certain combination of organelles, the apical complex, distinguishes this clade Apical complex is usually for penetrating host cell  The apicoplast, a modified plastid, may be ringlike, tubular or filamentous Mostly intracellular Uninucleated Form spores (sporozoites) at some stage in their life cycle  Parasites of vertebrates and invertebrates which cause serious disease of domestic animals and humans. It has a very complex life cycle that comprise of asexual (schizogony, sporogony) and sexual (gametagamy) phases that require two host E.G. Cryptosporidium, Toxoplasma, Plasmodium, Babesia, Isospora, Cyclospora Life cycle of Plasmodium  Crytoporidium is another Apicomplexan protozoa that causes chronic diarrhea in immunosuppressed individuals Toxoplasmosis caused by Toxoplasma results when meat containing encysted merozoites are eaten raw or poorly cooked And when oocyst are ingested with food contaminated by cat feces  Most Toxoplasmosis infections are asymptomatic In pregnancy congenital toxoplasmosis may develop: – Stillbirths – Spontaneous abortions Surviving fetuses show signs of mental retardation and epileptic seizures.  Coccidiosis is generally applied only to infections with Eimeria or Isospora. Humans can be infected with species of Isospora, but there is usually little disease. However, Isospora infections can be very serious in AIDS patients. Some species of Eimeria may cause serious disease in some domestic animals. Symptoms usually include severe diarrhea or dysentery  Sporogony Sporozoite  Domian EUKARYOTA Superphylum ALVEOLATA Phylum APICOMPLEXA Class Coccidea Order HAEMOSPORORIDA Family PLASMODIIDAE Genus PLASMODIUM Species falciparum  Stramenopiles Stramenopile refers to their characteristic flagellum, which has numerous fine, hairlike projections In most stramenopiles, the hairy flagellum is paired with a shorter smooth flagellum The cells are surrounded by plasma membrane, which may be supported by silica (silicon dioxide), calcium carbonate or proteinaceous shells, scales, or tests.  Almost all species posses unique, complex, three-part tubular hairs on the flagella at some stage in life cycle. Most exhibit heterokont flagellation (i.e., with two flagella, one directed anteriorly, one directed posteriorly). Sometimes only the reproductive cells are flagellated and the trophic cells lack any obvious mode of locomotion.  Mitochondria have short tubular cristae This clade contains forms that are photosynthetic, others are ingesting heterotrophs, and still others are saprophytic The clade include opalinids, diatom, Oomycetes and brown algae  Opalinata Opalinids, once thought to be modified ciliates are now placed in Stramenopiles. Their inclusion is based primarily on analyses of DNA sequence data Members are commensals in the rectum of frogs & toads Opalinids are thought to have lost their flagellation and replaced with rows of cilia  Almost all are endosymbiotic in the hindgut of anurans where they ingest dissolved material Some opalinids are binucleate, others are multinucleate, but all are homokaryotic or monomorphic Their numerous oblique rows of cilia clearly differ from the rows in ciliates in that they lack the kinetidal system.  There is no cytostome Sexual reproduction is by syngamy and asexual reproduction is by binary fission During asexual reproduction, the fission plane parallels the oblique ciliary rows; thus it is longitudinal (as it is in flagellates) rather than transverse (as it is in ciliates). Opalina ranarum  Nuclei Lines of Endo-plasm cilia Ecto-plasm Cilia Pellicle Opalina ranarum  Diatom Diatom are unicellular algae that have a unique glass-like wall made of silicondioxide embedded in an organic matrix. They are among the most abundant photosynthetic organisms both in the ocean and in lakes They are key components of marine ecosystems and, along with dinoflagellates and coccolithophores, contribute greatly to oceanic primary productivity  Benthic deposits of the siliceous shells of dead marine diatoms can, over geologic time, result in massive uplifted land formations that are n1ined as diatomaceous earth Diatomaceous earth sediments are mined for their quality as a filtering medium and for many other uses. It is estimated that diatom alone account for up to 20% of global carbon fixation  Diatom act as carbon sink thereby playing a great role in ameliorating global warming. Carbon in their bodies remains at the ocean floor for some time, rather than being released immediately as CO2 by decomposers. Because their shells (frustules) are composed of silica, they are also extremely important for the biogeochemicalcycling of silicon  On the other hand a few marine diatoms produce toxins similar in potency to those seen in some dinoflagellates. Diatom have caused deaths of sea lions, seabirds, fish and shellfish. Diatoms in the genus Pseudonitzschia are capable of producing the neurotoxin, domoic acid that can accumulate in the food chain and responsible for neurological disorders and memory loss called amnesic shellfish poisoning, or ASP). Silicious skeleton of Pennate diatom Tubular diatom the centric diatom Navicula sp Aulacosella Actinocyclus sp Diatom  Brown algae Brown algae also known seaweed (kelp) is a multicellular protists which form an integral base to many coastal food webs Algin, extracted from seaweed is used as an emulsifier in many thing from paint to babyfood to cosmetics  Oomycetes Oomycetes include the water molds, the white rusts, downy mildews, the potato blight. Although oomycetes descended from plastid- bearing ancestors, they no longer have plastids and do not perform photosynthesis. Instead, they typically acquire nutrients as decomposers or parasites. Most water molds are decomposers that grow as cottony masses on dead algae and animals  Based on their morphology, these organisms were previously classified as fungi For example, many Oomycetes have multinucleate filaments (hyphae) that resemble fungal hyphae The devastating Irish potato blight disease that resulted in famine of the nineteenth century was caused by an Oomycete, Phytophthera infestans  RHIZARIA Both Rhizarians and Amoebozoans use pseudopods for locomotion. Pseudopods are flowing projections of cytoplasm that extend to pull the organism forward. Amoeboid motion was once used as a trait to group protists, but the inclusion of molecular data in phylogenetic reconstructions led to the realization that locomotion alone was not a useful trait in evolutionary analyses.  Rhizarians are amoebas and flagellated protists that feed using threadlike pseudopodia. Within the Rhizaria, three distinct monophyletic groups have been identified: Radiolaria, Foraminifera and Cercozoa They are usually testate. Some have the test external and multi-chambered. While others have their skeleton internally placed.  Cercozoa The group is heterogeneous in terms of morphology. There are flagellated and ameboid members. Ameboid cercozoans also vary in pseudopodia formed: axopodia are made in phaeodarians and desmothoracids, but other members of the group make filopodia Ameboid members of the group may be naked or testate  Euglypha, is a testate cercozoan which makes a test from collected particles while Clathrulina, makes a siliceous capsule Phaeodarians, have an amorphous silica skeleton with magnesium, calcium, and copper added. Cercozoans are equally heterogeneous in lifestyle. There are photosynthetic members such as the chlorarachniophytes, which are naked green amebas with filopodia.  Other members are free-living heterotrophs, and still others, such as plasmodiophorids and haplosporidians, are parasites. Plasmodiophorids, once thought to be fungi, are obligate intracellular parasites responsible for crop damage. Granuloreticulosea (Foraminifera) Characteristic of the group are pore-studded shells (called tests) composed of organic materials usually reinforced with grains of calcium carbonate, sand, or even plates from shells of echinoderms or spicules from sponge skeletons Foraminiferans secrete many chambered tests made of calcium carbonate, although they sometimes accumulate silica, silt, and other foreign materials  The individual chambers of these tests are often demarcated from each other by perforated septa. Thin, extensively branching pseudopodia called reticulopodia, project from minute openings in the test, forming dense pseudopodial networks used primarily for food capture.  Repeated extension and shortening of the pseudopodia also permit slow crawling over the ocean bottom. Foraminiferans feed on a remarkable variety of food, including other protists, small metazoans, fungi, bacteria, and organic detritus. In addition, some species house photosynthesizing symbionts, including dinoflagellates, Polystomella strigillata Cibicides labatulus  Others can take up dissolved organic material from seawater Most foraminiferans live on the ocean floor in incredible numbers Dead foraminiferans have been sinking to the bottom of the ocean, building up a characteristic ooze rich in lime and silica  Of practical importance are the limestone and chalk deposits that were laid down by the accumulation of foraminiferans when sea covered what is now land. Since fossil foraminiferans can be found in well drillings, certain foraminiferan fossils are used as fairly reliable indicators of likely places to drill for oil  Radiolaria Radiolarians are marine testate amebas with axopodia (pseudopodia with thin, radiating microtubules that give a spiny, rayed appearance to many species) All radiozoans possess a rigid endoskeleton composed either of silica (in radiolarians) or strontium sulfate (in acantharians) All radiolarians and most acantharians are planktonic, passively carried about by ocean currents (planktonic).  Many species possess symbiotic algae getting some of their nutritional requirements through photosynthesis. They also feed as carnivores, capturing microscopic prey with the cytoplasm that flows along their axopods. The radiolarian body is generally spherical and divided into an intracapsular zone and an extracapsular zone by a perforated, spherical membrane or capsule.  Food vacuole formation and digestion occur in the extracapsular region. Because of their siliceous skeletons, radiolarians are prominent in the fossil record In contrast, acantharians have left no fossil record, as the strontium sulfate supports degrade soon after the organism dies. Radiolarian Actinosphaerium sol Unikonta  Amoebozoa The clade includes many species of amoebas that have lobe- or tube-shaped pseudopodia (Lobopodia) rather than the threadlike pseudopodia found in rhizarians. Most amoeba are free-living, but some are parasitic. Amoebozoans include tubulinids, slime molds, and entamoebas.  Tubulinea Large and varied group of amoebozoans that have lobe- or tube-shaped pseudopodia. These unicellular protists are ubiquitous in soil as well as freshwater and marine environments. Most are heterotrophs that actively seek and engulf bacteria and other protists by phagocytosis; e.g Amoeba proteus, Some tubulinids also feed on detritus  Some members referred to as naked amoebas lack a test (shell) or other supporting structures Others possess test which may be calcareous, proteineous, siliceous or chitinous. Other test may compose of sand and debris cemented into a secreted matrix  Large opening in the shell permit extension of the body and pseudopodia Testate amebas with lobose pseudopodia, include Arcella and Diffligia while naked lobose amebas, include Chaos carolinense, Amoeba proteus, and members of genus Acanthamoeba Amoeba proteus Difflugia oblongata  Growth & multiplication is by binary fission involving nuclear division by mitosis followed by cytoplasmic division Binary fission occurs when an aboeba reaches a certain size limit Triggered off when the surface area : volume ratio and / or when cytoplasmic volume : nuclear volume ratio reach a limit.  Under unfavourable conditions Amoeba forms cyst & remain inactive , until moisture or warm temperature are restored There may be sporulation in other species like Entamoeba histolytica which undergo spore formation No sexual reproduction is known to occur  Entamoebida Whereas most amoebozoans are free-living, those that belong to the genus Entamoeba are symbiotic parasites. They infect all classes of vertebrate animals as well as some invertebrates. Humans are host to at least six species of Entamoeba.  While Entamoeba coli is a commensal species that feed on bacteria and intestinal debris, E. histolytica, is known to be pathogenic. Both leave as cyst in feces and reinfection is via the mouth E. histolytica causes amoebic dysentery and is spread via contaminated drinking water, food, or eating utensils.  It causes inflammation and ulceration of the lower intestinal tract and a debilitating diarrhea that includes blood and mucus characterize dysentery Amoebic dysentery is responsible for up to 110,000 deaths worldwide every year, being the third leading cause of death.  Acanthamoebida Acanthamoeba possess both flagellated and amoeboid form and are facultative parasites of humans. Acanthamoeba causes meninggoencephalitis while Naegleria fowleri infects the cornea leading to inflammation and opacity  Mycetozoa(Slime molds) Once were thought to be fungi because they produce fruiting bodies that aid in spore dispersal. Through DNA sequence analyses that resemblance is a case of evolutionary convergence. Slime molds have diverged into two main branches;  Plasmodial Slime Molds Brightly coloured (yellow or orange) As they grow, they form a mass called a plasmodium, which can be many centimeters in diameter. Despite its size, but a single mass of cytoplasm that is undivided by plasma membranes and that contains many nuclei. The “supercell” is the product of mitotic nuclear divisions that are not followed by cytokinesis.  The plasmodium extends pseudopodia through moist soil, leaf mulch, or rotting logs, engulfing food particles by phagocytosis as it grows. If the habitat dries up or there is no food left, the plasmodium stops growing and differentiates into fruiting bodies that function in sexual reproduction.  Cellular Slime Molds The cellular slime molds have intriguing life cycle. The feeding stage of these organisms consists of solitary cells that function individually. However when food is depleted, the cells form a slug-like aggregate that functions as a unit. Unlike the feeding stage (plasmodium), these aggregated cells remain separated by their individual plasma membranes. Ultimately, the aggregated cells form an asexual fruiting body Life cycle of cellular slime mold SAR  References Invertebrates--- R. C. BRUSCA, W. MOORE, S. M. SHUSTER, Intergrated Principles of Zoology.---- Hickman, Roberts & Larson