Protozoans

• The first evidence of life were prokaryotic bacteria-like cells that date back to 3.5 billion years ago.
• These early cells diversified and formed two prokaryotic groups: archaea and bacteria.
• The ancestor of eukaryotes formed through symbiogenesis, where a cell of one prokaryotic lineage engulfed, but did not digest, a cell from another prokaryotic lineage.
• The engulfed cell eventually became an organelle inside the host cell resulting in the origin of complex eukaryote cells.
• Primary endosymbiosis is the modification of an engulfed prokaryote into an organelle within a prokaryotic host.
• Aerobic bacteria were engulfed by host to become mitochondria found in modern eukaryotic cells.
• Engulfed photosynthetic bacteria evolved into chloroplasts.
• Unicellular eukaryotic organisms were called protozoa due to animal-like features, including lack of a cell wall, having at least one motile stage in life cycle, and most ingesting their food.
• Protozoa are very important components of ocean soil deposits formed over millions of years.
• At least 10,000 species of protozoa are symbiotic in or on other plants or animals, potentially being mutualistic, commensalistic, or parasitic.
• Trichocysts in ciliates expel long thread-like structures when stimulated, believed to be a defensive mechanism.
• Ichthyophthirius sp is a parasitic ciliate that lives in the skin of fish.
• New additions to the Stramenopile group include Opalinids, Labyrinthulids, and Oomycetes.
• Stramenopiles include plant-like brown algae, yellow algae, and diatoms that can do photosynthesis, while others are heterotrophs.
• Phylum Ciliophora has a body surface covered with cilia that beat in a coordinated, rhythmical manner.
• Oomycetes, presumed to be fungi at first, are well known for causing the potato blight that led to the Irish potato famine.
• Ciliates are always multinucleated, with macronuclei that transcribe genes, have metabolic and developmental functions, maintain all visible traits like the pellicle, and divide amitotically.
• Heliozoans, testate amebas with axopodia from the group Actinophryida, are now grouped with Stramenopiles due to recent molecular phylogeny.
• Micronuclei, which are never transcribed, are involved in sexual reproduction and give rise to macronuclei after exchange with other micronuclei, divide mitotically.
• Three traditional phyla are found in Alveolata: Phylum Ciliophora, Phylum Dinoflagellata, and Phylum Apicomplexa.
• Labyrinthulids, also known as slime nets, can be commensal or mutualistic with plants, can be parasitic on eel grass and turf grass.
• Ciliates are the most structurally diverse and specialized protozoans, are usually solitary and motile, and live in freshwater or marine habitats.
• Entodinium sp and Nyctotherus sp live in the digestive tracts of ruminants, frogs and toads, respectively.
• Stramenopiles are heterokont flagellates with two different flagella, both inserted in the anterior end but one is long and hairy while the other trails behind and is short and smooth.
• Toxicysts in ciliates release poison that paralyzes prey of carnivorous ciliates, with dinoflagellates generally also having trichocysts.
• Alveolata is a clade united by the shared presence of alveoli, which are membrane-bound sacs beneath the cell membrane.
• Many ciliates are commensal, but some are parasitic, with Balantidium coli living in the intestine of humans, pigs, rats, and other mammals.
• Opalinids are commensals to frogs and were once thought to be modified ciliates.
• Bikonts includes all taxa, other than unikonts, with two flagella.
• Eukaryotic Supergroups were combined using molecular data sets and the pathway of endosymbiont transfers.
• Unikonts includes Amebozoa and Opisthokonta.
• SAR, or Stramenopiles, Alveolata, and Rhizaria, is a group with some support.
• Opisthokonta contains metazoan animals, fungi, and some unicellular taxa.
• Choanoflagellates are solitary or colonial cells that are most likely a sister taxon to animals.
• Opisthokonta is a clade characterized by flattened mitochondrial cristae and the presence of one posterior flagellum on flagellated cells.
• Microsporidians are intracellular parasitic fungi that are among the best known unicellular taxa in the Opisthokonta clade.
• There are multiple phyla, with perhaps more than 60 exclusive eukaryotic clades, and taxonomic classification cannot rely on nutritional or locomotion modes for clear differences between unicellular eukaryotic groups.
• Plantae includes all land plants.
• Fornicata includes Retortamonads and Diplomonads.
• Excavata includes Fornicata, Parabasalea, Heterolobosea, and Euglenozoa, and is also a group with some support.