In this article we will discuss about the various examples (classes and subclasses) of protozoa.
Phylum I. Sarcomastigophora:
Locomotory organelles flagella or pseudopodia or both. Nucleus single type except in developmental stages of certain foraminifera. Spore formation absent. Sexuality often present, essentially syngamy.
Subphylum I. Mastigophora:
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Solitary or colonial; flagella one or more in trophozoites; asexual reproduction by symmetrogenic binary fission; nutrition phototrophic or heterotrophic.
Class 1. Phytomastigophora (plantlike flagellates):
Mostly free-living; some ectoparasitic and very few are endoparasitic; flagella one or two; amoeboid forms common in some groups; chromatophores present; sexual reproduction occurs in some. Examples: Euglena, Crypto monas, Colacium, Haplazoon, Volvox, etc.
Class 2. Zoomastigophora (animal like flagellates):
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Mostly parasitic; flagella one to many; amoeboid forms with or without flagella in some groups; chromatophores absent; sexual reproduction is known in some. Examples: Trypanosoma, Leishmania, Trichomonas, Giardia, Trichonympha, etc.
Subphylum II. Opalinata:
Parasitic; cilia-like locomctory organelles over the entire body surface in oblique rows; cytostome absent; nuclei single type and two or many; asexual reproduction usually by symmetrogenic binary fission; life cycles involve syngamy with anisogamous flagellated gametes. Examples: Opalina, Protooplina, etc.
Class Opalinatea:
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(Characters similar to those of the subphylum).
Subphylum III. Sarcodina:
Mostly free-living; body naked or with external and internal tests or skeletens; typical pseudopodia present; flagella, when present, restricted to developmental stages; asexual reproduction by fission; sexual reproduction, if present with flagellate or, more rarely, amoeboid gametes.
Superclass I. Rhizopoda:
Locomotion by lobo podia, filopodia or reticulopodia or by protoplasmic flow without production of discrete pseudopodia.
Class 1. Lobosa:
Pseudopodia lobose, rarely filiform or anastomosic; usually uninucleate.
Subclass i. Gymnamoebia:
Test absent. Examples: Amoeba, Entamoeba, Acanthamoeba, etc.
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Subclass ii. Testacealobosia:
Body enclosed in a test, tectum or other complex membrane, external to plasma membrane. Examples: Arcella, Trichosphaeriumor, etc.
Class 2. Acarpomyxea:
Small plasmodia or much expanded similar uninucleate forms, usually branched, sometimes forming reticulum of coarse branches; no test; no spore or fruiting bodies known. Examples: Leptomyxa, Rhizamoeba, etc.
Class 3. Acrasea:
Uninucleate amoebae with eruptive, lobose pseudopodia; amoebae aggregating to form pseudo plasmodium which gives rise to fruiting bodies without stalk tube; sexuality unknown. Example: Acrasis.
Class 4. Eumycetozoea:
Myxamoebae with filiform sub-pseudopodia; flagella, when present non-mastigonemate, in unequal, less often equal, apical pair; aerial fruiting bodies.
Subclass i. Protosteliia:
Trophic stage varying from single amoeba to plasmodia which lack shuttle streaming; flagellate cells present or absent; fruiting bodies consist of one to several spores on narrow, hollow stalk. Example: Ceratiomyxa.
Subclass ii. Dictyosteliia:
Amoebae aggregate to form multicellular pseudo plasmodium that gives rise to multispored fruiting body; stalk tube present; no flagellate cell. Example: Dictostelium.
Subclass iii. Myxogastria:
Major trophic stage multinucleate Plasmodium typically with shuttle streaming; fruiting bodies multispored; flagellate cells present; syngamy and meiosis in life cycle. Examples: Echinostelium. Licea, etc.
Class 5. Plasmodiophorea:
Obligate intracellular parasites with minute plasmodia; zoospores produced in zoosporangia and bearing an anterior pair of unequal, non-mastigonemate flagella; resting spores formed in compact sori or loose clusters within host cells. Examples: Plasmodiophora, Sorosphaera, etc.
Class 6. Filosea:
Hyaline, filiform pseudopodia, often branched, sometimes anastomosing; no spores or flagellate stages known. Examples: Nuclearia, Euglypha, etc.
Class 7. Granuloreticulosea:
Delicate, finely granular or hyaline reticulopodia or, rarely, finely pointed, granular but anastomosing pseudopodia. Examples: Allogromia, Ammonia, Elphidium, etc.
Class 8. Xenophyophorea:
Multinucleate plasmodium enclosed in branched tube system composed of transparent organic substance; numerous barite crystals in cytoplasm; faecal pellets retained outside organic tube system as conspicuous, dark masses; test of foreign matter surrounding tube system and faecal pellet masses; marine. Examples: Psammina, Stamnophyllum, etc.
Superclass 2. Actinopoda:
Typical fleating forms; body spherical; naked or with test; pseudopodia delicate and radiose; reproduction by both asexual and sexual means; gametes usually flagellated.
Class l. Acantharea:
Strontium sulphate skeleton, usually composed of 20 radial or 10 diametrical spines; sometimes many more spines randomly oriented; extracellular outer (cortex) and inner envelopes usually present; inner envelope (capsular membrane) often close to central cell mass; marine, usually planktonic. Examples: Acanthochiasma, Amphilithium, Actinelius, etc.
Class 2. Polycystinea:
Siliceous skeleton present in most species, made up usually of solid elements consisting of one or more latticed shells with or without radial spines or, of one or more isolated spicules; capsular membrane composed usually of grossly polygonal plates and many containing more than 3 pores; axonemes often originate from axoplast in endoplasm; marine, planktonic. Examples: Orescena, Coccodisms. Plagonium, etc.
Class 3. Phaeodarea:
Skeleton (sometimes absent) of mixed silica and organic matter, consisting usually hollow spines and/or shells; very thick capsular membrane with astropyle (functioning as cytopharynx) at one pole; ectoplasm with phaeodium (group of dark corpuscles and debris); marine, planktonic. Examples: Aulacontha, Castanella, Medusetta, Concharium, Coelodendrum, etc.
Class 4. Heliozoea:
Without central capsule; skeletal structures if present, siliceous or organic; axopodia radiating on all sides; most species fresh water, some marine. Examples: Clathrulina, Actinophrys, Acanthocystis, etc.
Phylum II. Labyrinthomorpha:
Trophic stage, ectoplasmic network with spindle-shaped or spherical, non-amoeboid cells; in some genera amoeboid cells move within network by gliding; heterokont zoospores produced by most species; saprobic and parasitic on algae, mostly in marine and esturian waters.
Class l. Labyrinthulea:
Characters similar to those in the phylum. Examples: Labyrinthula, Thravstochytrium, etc.
Phylum III. Apicomplexa:
Presence of apical complex (visible only in electron microscopy); the complex includes a polar ring(s), micronemes, rhoptries, subpellicular microtubules, micropore(s) and a conoid at the apical terminal; cilia absent; syngamy occurs; all are parasites.
Class l. Perkinsea:
Spherical enclosing several daughter cells known as zoospores; zoospore flagellated. Reproduction by multiple fission of the original single nucleus; spores with very large, partially eccentric vacuole; usually oval nucleus contains a compact, deep staining endosome. Example: Parkinsus (parasite in oyster).
Class 2. Sporozoea:
Parasitic; nucleus single type; typical simple spores present; syngamy associated with sexual reproduction, when present; infective sporozoites result from sporogony; locomotion of adult by body flexion, gliding or, undulation of longitudinal ridges.
Subclass i. Gregarinia:
Mature gametes large, extracellular; mucron or epimerite in mature organism; generally syzygy of gametes, isogametes or nearly so, with similar members of male and female gametes produced by gamonts; zygotes form oocysts within gametocytes; life cycle consists of gametogony and sporogony; parasites in digestive tract or body cavity of invertebrates and lower chorates. Examples: Monocystis, Stenophora, Gregarina, etc.
Subclass ii. Coccidia:
Gamonts ordinarily present; mature gamonts small, typically intracellular, without mucron or epimerite; syzygy generally absent, if present, involves markedly anisogamous gametes; life cycle characteristically consisting of merogony, gametogony and sporogony; most species parasites in invertebrates; Examples : Grellia, Haemogregarina, Eimerina, Isospora, Toxoplasma, Sarcocystis, Haemoproteus, Plasmodium, Leucocytozoon, etc.
Subclass iii. Piroplasmia:
Pyriform, round, rod-shaped or amoeboid; conoid absent; no oocysts, spores and pseudocysts; flagella absent; usually without subpellicular microtubules, with polar ring and rhoptries; locomotion by body flexion, gliding, or in sexual stages, by large axopodium-like strahlen; asexual and probably sexual reproduction; parasitic in erythrocytes and sometimes in other circulating and fixed cells; known vectors are ticks. Examples: Babesia, Theileria, etc.
Phylum IV. Microspora:
Unicellular spores, each with imperforate wall, containing one uninucleate or di-nucleate sporoplasm and simple or complex extrusion apparatus always with polar tube and polar cap; without mitochondria; obligatory intracellular parasites in nearly all major animal groups.
Class l. Rudimicrosporea:
Spore with simple (rudimentary) extrusion apparatus consisting of polar cap and thick (manubroid) polar tube extending backward from cap, bending laterally and terminating in a funnel (infundibulum); sporulation sequence with dimorphism, occurring either in parasitophorous vacuole or in the thick-walled cyst; hyperparasites of gregarines in annelids. Examples: Amphoacantha, Metehnikovella, etc.
Class 2. Microsporea:
Spore with a complex extrusion apparatus of Golgi origin, often including polaroplast and a posterior vacuole in addition to polar tube and polar cap; polar tube typically filamentous, extending backward from the polar cap and coiling around inside of spore wall; parasites of every major group of animals, from protozoon’s to man—especially abundant in arthropods, fish and mammals; undergo both schizogony and sporogony; spores are small, 3-6 µm, spherical, ovoid or cylindrical; hollow polar filament in resting spore remain tightly coiled surrounding the nucleus and most of the cytoplasm; in some two nuclei are associated intimately and known as diplokaryon. Examples: Thelohania, Nosema, etc.
Phylum V. Ascetospora:
Spore multicellular (or uninucleate?); with one or more sporoplasms; without polar capsules or polar filaments; all parasitic.
Class l. Stellatosporea:
Haplosporosomes present; spores with one or more sporoplasms. Examples: Marteilia, Minchinia, Haplosporidium, etc.
Class 2. Paramyxea:
Spore bi-cellular, consisting of parietal cell and one sporoplasm; spore without orifice. Example: Paramyxa.
Phylum VI. Myxozoa:
Spores of multicellular origin, with one or more polar capsules and sporoplasms; with 1, 2 or 3 (rarely more) valves; all species parasitic.
Class l. Myxosporea:
Spores with one or two sporoplasms and 1-6 (typically two) polar capsules, each with a coiled polar filament; filament function probably anchoring; spore membrane generally with two, occasionally up to six valves; trophozoite, main stage of proliferation well developed; coelozoic or histozoic in cold blooded vertebrates. Examples: Myxidium, Sphaeromyxa, Ceratomyxa, Henneguya, Myxobolus, Thelohanellus, etc.
Class 2. Actinosporea:
Spores with three polar capsules, each enclosing a coiled polar filament; membrane with three valves, several to many sporoplasms; trophozoite stage reduced; proliferation during sporogenesiparasitic in invertebrates, specially in annelids.
Subclass 1. Actinomyxia:
Spores with three polar capsules, each enclosing a polar filament; membrane with three valves; several to many sporoplasms. Example: Triactinomyxon.
Phylum VII. Ciliophora:
Simple cilia or compound ciliary organelles typical, at least in one stage of life cycle; subpellicular infraciliature present even when cilia absent; two types of nuclei, with rare exception; binary fission transverse, basically homothelogenic and generally parakinetal; budding and multiple fission also occur; sexuality involves conjugation, autogamy and cytogamy; nutrition heterotrophic; typical contractile vacuole present; most species free- living but many commensal, some true parasitic, and a large number symphorionts on variety of hosts.
Class l. Kinetofragminophorea:
Oral infraciliature only slightly distinct from somatic infraciliature and differentiated from anterior parts or, other segments of all or some of somatic kinetics; cytostome often apical (or sub-apical) or mid-ventral, on surface of the body or at the bottom of the atrium or vestibulum; cytopharyngeal apparatus commonly prominent; compound ciliature, oral or somatic, typically absent.
Subclass i. Gymnostomatia:
Cytostomal area superficial, apical or sub- apical; circumoral infraciliature without kinetosomal differentiation other than closer packing of kinetosomes, insertion of supplementary segments of kinetics or, pairing (not as dyads) of kinetosomes; cytopharyngeal apparatus rhabdos type; toxcysts common, somatic ciliation usually uniform. Examples: Bundleia, Didesmis, Metacystis Didinium, Amphileptus, Stephanopogon, Laxades, etc.
Subclass ii. Vestibulifera:
Apical or near apical vestibulum commonly present, equipped with cilia derived from anterior parts of somatic kinetics and leading to cytostome; stomatogenesis, sometimes involving two anlagen’s; cytopharyngeal apparatus resemble rhabdos; free-living or parasitic, especially in digestive tract of vertebrates. Examples: Balantidium, Isotricha, Entodinium, Colpoda, etc.
Subclass iii. Hypostomatia:
Cytostome nonpolar, on ventral surface; body cylindrical or flattened dorsoventrally, often with reduction of somatic ciliature; cytopharyngeal apparatus typically of cyrtos type; oral area may be sunk into citrium; some species astomatous; free-living or ecto- or endo-commensals, principally of invertebrates. Examples: Leptopharynx, Nossulopsis, Hartmannula, Isochona, Opalinopsis, etc.
Subclass iv. Suctoria:
Suctorial tentacles generally multiple (polystomy) containing haptocysts; adult sessile and sedentary, seldom with cilia; reproduction by budding; stalk commonly present, non-contractile, produced by scupoloid; conjugation often involving micro and macro-conjugant; migratory larva ciliated, without tentacles or stalk; marine and fresh water, with wide distribution, occasionally endo-commensal. Examples: Podophyra, Acineta, Tokophyra, Discophyra, Heliophyra, etc.
Class 2. Oligohymenophorea:
Oral apparatus, at least partially in buccal cavity, generally well-defined, although absent in one group; oral clearly distinct from somatic ciliature, consisting of paroral membrane (stichodyad) on right side and a small number of compound organelles on left side; cytostome usually ventral and/ or near anterior end at the bottom of buccal or infundibular cavity; colony formation common in some groups.
Subclass i. Hymenostomatia:
Body ciliation often uniform and heavy; buccal cavity, when present, ventral; kinetodesmata regularly present, usually conspicuous; sessile forms with stalk; colony and cyst formation relatively rare; fresh water forms predominant. Examples: Colpidium, Tetrahymena, Paramoecium, Conchophthirus, Pleuronema, Anoplophrya, etc.
Subclass ii. Peritrichia:
Oral ciliary field prominent, covering apical end of body and dipping into infundibulum; paroral membrane, generally called ‘haplokinety’ and adoral membranelles, ‘polykineties’, becoming ‘peniculi’ in infundibulum present; somatic ciliature reduced to temporary posterior circlet of locomotors cilia; widely distributed species, many stalked and sedentary, others mobile, all with aboral scopula; myonemes associated with strong contractility of stalk or parts of the body; conjugation total, involving fusion of macro and micro-conjugants. Examples. Vorticella, Zoothamnium, Trichodina, etc.
Class 3. Polymenophorea:
Well-developed, conspicuous adoral zone with numerous buccal or peristomial organelles, often extending out on to body surfaces; on right side, one or several lines of paroral ciliature; stomatogenesis parakinetal or apokinetal; somatic ciliature complete or reduced or, appearing as cirri; cytostome at the bottom of buccal cavity or infundibulum; cytoproct often absent; large and commonly free-swimming forms in great variety of habitats.
Subclass 1. Spirotricha:
Characters similar to those of the class. Examples: Stentor, Nyctotherus, Folliculina, Saprodinium, Tintinnopsis, Stylanchia, etc..