Phylum Classification
Protista, commonly known as Protists, are an extremely diverse group of unicellular or unicellular-colonial Eukaryotic organisms. The phylum possesses a complex intracellular structure which distinguishes Protists from other single celled organisms. The complicated internal structure is essential for cellular function. Protists maintain their functionality by substituting multiple organelles, mitochondria, and, in some species, nuclei for the specialized cells which multicellular organisms utilize for similar processes.
Protists employ autotrophic, heterotrophic, or mixotrophic methods to acquire nutrients. Heterotrophs secure nutrients from organic material in their environment. These organisms use their cell body to surround and swallow organic material creating food vacuoles, or absorb nutrients from their surroundings by osmosis. Cilia may be used to assist particle movement into oral grooves of certain species. Cilia, as well as flagella, are also utilized for motility. Autotrophs use photosynthesis to acquire their nutrients. Protists that use photosynthesis and phagocytosis are classified as mixotrophic organisms.
The primary mechanism for reproduction of Protista is asexual. Asexual mechanisms include, binary fission, multiple fission, plasmotomy, spore formation and budding. Some exclusive species sexually reproduce by syngamy or conjugation. There are seven major groups of Eukarya containing Protozoans: Amoebozoa, Opisthokonta, Excavata, Plantae, Rhizaria, Stramenopila, and Aveolata.
Class Amoebozoa
Amoebozoa is a large, diverse class of Protista that share general characteristics. One shared characteristic is a lobe, tube-shaped pseudopodia. The cellular structure of Amoebozoa lack a cell wall that allows the endoplasm to freely flow. This flexibility gives Amoebozoa the ability to use an amoeboid motion to move by using the pseudopodia that extend and retract to act as a “false foot”. Most species of Amoebozoa use phagocytosis as their primary mode of nutrition. The organism engulfs food particles and creates food vacuoles which digest and absorb the nutrients. The waste is then expelled using exocytosis. Some differences in characteristics include variations of asexual and sexual reproduction and life cycles.
Major subgroups of Amoebozoa include lobose amoebae, cellular slime mold, and plasmodial slime mold. Plasmodial slime mold is an important single celled decomposer organism which contains many nuclei.
Species Identification
Amoeba proteus
Video: The quick video depicts Amoeba movement using a light microscope under 4x magnification.
Slides: The prepared slide is Amoba proteus mounted and viewed under 40x magnification using a light microscope. The diagram is a labeled representation of the cell structure of a basic Amoebozaon.
Class Opisthokonta
Opisthokonta is another widely diverse group of Protista including animal and fungus. Opisthokonta are flagellated cells that propel themselves with a single posterior flagellum, and do not contain an anterior flagella like most other eukaryote groups. The organisms consist of collagen as one of the main components of the extracellular matrix. The only discriminating characteristics of Opisthokonta are the platycristate mitochondria and flat, membrane-bound cavities that make a Golgi apparatus.
Choanoflagellates are a noteworthy clades of Opisthokonta if one is interested in marine invertebrates. Choanoflagellates are free-living unicellular and colonial eukaryotes. The choanocytes of choanocytes obsevered in Porifera.
Class Excavata
Organisms classified as Excavata are asymmetrical, single-celled organisms with an excavated feeding groove apparent on one side of the organism. These free-living species are either parasites, heterotrophic predators, or photosynthetic species that may share a mutualistic relationship with other organism. Various feeding behaviors, flagellar structures, and mitochondrial complexity further distinguish Excavata organisms into three subgroups: Parabasalids, Diplomonads, and Euglenids.
Parabasalids are Excavata organisms that either share a symbiotic relationship with other organisms, or are parasitic. Parabasalids use flagella to move that is assisted by an undulating membrane. These organisms lack feeding groove that appears to be a secondary loss in the evolution of Excavata. Parabasalids are anerobic organism that have also evolutionarily replaced the mitochondria with a hydrogenosome. Hydrogenosomes are structures that function anaerobically and produce hydrogen gas as a byproduct.
Diplomonads, commonly identified as intestinal parasites, also have a replaced mitochondria. However, instead of a hydrogenosome, diplomonds posses a mitosome that are essentially nonfunctional remnant mitochondrial organelles. Diplomonads obtain their energy by interacting with their anaerobic environment and using alternative pathways. Arranged asymmetrically in the organisms body are two nuclei, each with four flagella used for locamotion.
Euglenids are a diverse group of Excavata that include parasites, heterotrophs, autotrophs, and mixotrophs. Primary modes of nutrient intake include diffusion and phagocytosis, but many of the Euglenids produce their own food through photosynthesis. Euglenids propel themselves towards light sources using two long flagella. They possess a primitive ocular organ called an eyespot that is used to sense these light sources. One feature that diversifies Euglenids from Parabasalids and Diplomonads is the presence of a pellicle giving them a variety of rigidity and shape.
Species Identification
Euglena gracilis
Video: The video demonstrates the movement of Euglena gracilis through a substrate. Their quick movement is facilitated by a flagella.
Slides: Euglena gracilis drawings show the basic structure of the organism and a labeled diagram presents information of approximate locations of organelles.
Class Plantae
Plantae, also known as Viridiplantae, is a group of land plants and green algae consisting of Chlorophytes and Charophytes. These primarily aquatic organisms contain cellulose in their cell walls and primitive chloroplasts, making them almost exclusively photoautotrophic. The organisms of this class may either be multicellular, solitary unicellular, or colonial unicellular.
Species Identification
Volvox carteri
Video: A volvox colony is shown as it moves in a circular fashion as the flagella from individuals in the colony beat to move the colonial mass.
Slides: A volvox colony drawing shows the single cells, as well as daughter colonies, within the colony. The labeled diagram gives an overall view of a colony, a close up to the cells that form the colony, and the parts of a single volvox cell.
Class Rhizaria
The premise of Rhizarian classification is exclusively based on rDNA sequences. The variety of morphological characteristics and biochemical features, so far, have not shown any uniting qualities between members of this group. Two major groups of Rhizarians are the Foraminiferans and Radiolarians.
Foraminiferans are marine organisms that are one of the most abundant protozoans. They secrete multi-chambered tests composed of calcium carbonate. A dense network of pseudopodia is formed through branches that emerge through pores in test.
Similar to the Foraminiferans, Radiolarians also secrete a multi-chambered test, but Radiolarians tests are composed of silica. Another distinguishing feature of these Rhizarians is that presence of an axopodia. The axopodia consists of a pseudopodia and its micro-tubular support system. Their body is divided into intra- and extra-capsular zones which house the nucleus and primitive digestive system respectively.
Species Identification
Radiolaria
Video: The video displays the slow movement of a radiolarian species.
Slides: The microscopic image depicts a typical radiolarian structure. The long cylindrical pointed axopodia is prominent and easily detectable. The labeled diagram shows a cross section of a typical radiolarian.
Foraminifera
Video: Here you can see a close up view of the reticulopodia of the foraminifera.
Slides: Multiple Polystomella strigillata are shown under a light microscope. A labeled diagram of a P. strigillata cross section is also shown.
Class Stramenopila
Stramenopila is a group of Protista generally inhabiting marine environments, although some live in soil. Subgroups of Stramenopila include diatoms, water molds, kelps, and brown algae. The organisms in this group are mainly photosynthetic, but some may obtain food through parasitic means.
Class Aveolata
The class Alveolates is a large and diverse group of Protista with a notable sac-like characteristic. Flattened vesicles are packed under the membrane forming a pellicle. Alveolates posses an oral groove to ingest food and expel waste through exocytosis. Aveolata may undergo asexual or sexual reproduction. The Alveolates are separated into three main subgroups; Ciliates, Dinoflagellates, and Apicomplexans.
The Ciliates are covered in cilia that are connected under the body surface by a infraciliature. The cilia are used for movement and for moving organic matter into oral grooves. Some species posses an undulated membrane, a flattened sheet of cilia, that moves as a single unit to propel the organism. Another feature that is particular to Ciliates is the formation of a pellicle. The pellicle serves as a supportive membrane that houses trichocytes. These trichocytes are organelles comprised of filaments that may be ejected from the pellicle for defense or assault. Ciliates contain both macronuclei and micronuclei. Macronuclei contain all of the DNA and RNA in an organisms, while the micronuclei are essential for reproduction. Ciliates may either produces asexually through binary fussion, or sexually through conjugation.
Dinoflagellates are characterized by the possession of two flagella. One flagella surrounds the cell in a transverse grooved center, and the other lies longitudinally. The orientation of the two flagella cause Dinoflagellates to have a particular whirling swimming pattern. Dinoflagellates are best known for their bioluminescent properties and mutualistic relationship with other organisms. The mutualistic relationship is viable due to the photosynthetic nature of most Dinoflagellates.
Apicomplexa is comprised of 6,000 endoparasitic species of Aveolata that are characterized by their apical complex. The apical complex is used to drill into the host organism. The Apicomplexa also possess a complex life-cycle that involve gametocyte and sporocyte stages, and a number of intermediate hosts.
Species Identification
Paramecium caudatum
Video: The video give some sense of the internal structure of Paramecium caudatum. The movement of these organisms is usually faster than what is depicted in video.
Slides: In the slide you can see a more stable representation of internal structure. The labeled diagram puts a labeled to the organelles shown in the slide.
Stentor coeruleus
Video: Here is a stentor that is detached from a substrate using cilia to propel itself through the environment.
Slides: A sketch of a typical stentor species is shown along with a diagram that labeled all structural parts of the organism.
Spirostomum sp.
Video: The floating snake like movement of a Spirostomum species.
Slides: A sketch of a typical Spirostomum species and a diagram labeling its major structural features.
Glossary of Terms
Additional Drawn Images
[1] Brusca, R.C., & Brusca, G.J.(2003). Invertebrates. Sunderland, MA: Sinauer Associates, Inc.
[2] Ruppert, E., Fox, R., & Barnes, R. (2004). Invertebrate zoology : A functional evolutionary approach (7th ed. ed.). Belmont, CA: Thomson-Brooks/Cole.
[3] Anderson, D. (2001). Invertebrate zoology. Melbourne: Oxford University Press.
[4] Meglitsch, P., & Schram, F. (1991). Invertebrate zoology (3rd ed. ed.). New York: Oxford University Press.
Academic Coursework 