Euglenozoa Characteristics

Euglenozoa

• Euglenozoa is a diverse clade that includes euglenids and kinetoplastids
• They have a spiral or crystalline rod of unknown function inside their flagella
• Euglenids have one or two flagella that emerge from a pocket at one end of the cell
• Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast
• They include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems

Kinetoplastids

• Include Trypanosoma gambiense, which causes sleeping sickness in humans
• Another pathogenic trypanosome causes Chagas’ disease leading to congestive heart failure

SAR Supergroup

• Some data suggest that SAR is monophyletic and originated by a secondary endosymbiosis event
• The proposed endosymbiont is a red alga
• This clade is controversial and includes alveolates and stramenopiles

Alveolata

• Have membrane-bounded sacs (alveoli) just under the plasma membrane
• The function of the alveoli is unknown
• Include dinoflagellates, apicomplexans, and ciliates

Dinoflagellates

• Have two flagella and each cell is reinforced by cellulose plates
• Are abundant components of both marine and freshwater phytoplankton
• Are a diverse group of aquatic phototrophs, mixotrophs, and heterotrophs
• Toxic “red tides” are caused by dinoflagellate blooms

Endosymbiosis and Protist Evolution

• Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell
• Mitochondria are believed to have evolved by endosymbiosis of an aerobic prokaryote
• Plastids are believed to have evolved by endosymbiosis of a photosynthetic cyanobacterium

Diversity

• It is no longer thought that Excavates are the oldest lineage of eukaryotes
• Many have been shown to have mitochondria and have been reclassified
• Our understanding of the relationships among protist groups continues to change rapidly
• One hypothesis divides all eukaryotes (including protists) into four supergroups

Excavates

• Some members have a feeding groove that appears like “excavated” from the surface
• Include diplomonads, parabasalids, and euglenozoans

Diplomonads

• Have modified mitochondria called mitosomes
• Derive energy from anaerobic biochemical pathways
• Have two equal-sized nuclei and multiple flagella
• Are often parasites, for example, Giardia intestinalis (also known as Giardia lamblia)

Parabasalids

• Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically
• Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females

Apicomplexans

• Are parasites of animals, and some cause serious human diseases
• Spread through their host as infectious cells called sporozoites
• One end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues
• Most have sexual and asexual stages that require two or more different host species for completion

Plasmodium

• Is the parasite that causes malaria
• Requires both mosquitoes and humans to complete its life cycle
• Approximately 900,000 people die each year from malaria
• Efforts are ongoing to develop vaccines that target this pathogen

Ciliates

• Are named for their use of cilia to move and feed
• Have large macronuclei and small micronuclei
• Genetic variation results from conjugation, in which two individuals exchange haploid micronuclei
• Conjugation is a sexual process, and is separate from reproduction, which generally occurs by binary fission

Stramenopila

• Include important phototrophs as well as several clades of heterotrophs
• Most have a “hairy” flagellum paired with a “smooth” flagellum
• Include diatoms, golden algae, brown algae, and oomycetes

Diatoms

• Are unicellular algae with a unique two-part, glass-like wall of hydrated silica
• Are a major component of phytoplankton and are highly diverse
• Fossilized diatom walls compose much of the sediments known as diatomaceous earth
• After a diatom population has bloomed, many dead individuals fall to the ocean floor undecomposed
• Reproduction is mainly asexual

Characteristics of Protists

• Protists are eukaryotic, meaning they have a nucleus and multiple membrane-bound organelles.
• They exhibit varied shapes, patterns, and organelles.

Historical Classification of Protists

• Protists were previously grouped into a single kingdom, but this was dismantled in the 1990s due to the lack of connection between organisms.
• Today, protists are classified into four supergroups: Excavata, SAR, Archaeplastida, and Chromalveolata.

Cell Structure and Nutrition

• Most protists are single-celled (unicellular), but some species form colonies or are multicellular.
• Protists have diverse subcellular structures, including organelles, which aid in survival.
• They can be photoautotrophs, heterotrophs, or mixotrophs, with varying modes of nutrition.

Modes of Nutrition

• Photoautotrophs use photosynthesis to produce energy, often with chloroplasts.
• Heterotrophs are unable to produce their own food and must ingest or absorb nutrients from their environment.
• Mixotrophs can switch between autotrophic and heterotrophic modes of nutrition.

Reproduction

• Some protists can reproduce asexually, while others use meiosis to produce nuclei for sexual reproduction.
• Some protists, like kelp, exhibit alternation of generations, where two distinct generations are needed to complete a life cycle.

Endosymbiosis

• Endosymbiosis is the process by which some eukaryotic cells engulfed bacteria, leading to the formation of organelles like mitochondria and chloroplasts.
• Primary endosymbiosis occurred when a heterotrophic eukaryote consumed a cyanobacterium, leading to the formation of red or green algae.
• Secondary endosymbiosis occurred when a heterotrophic eukaryote consumed a cell with a chloroplast, leading to the formation of diverse chloroplasts in protists.

Classification of Protists

• The four supergroups of protists (Excavata, SAR, Archaeplastida, and Chromalveolata) have distinct common ancestors and are believed to be polyphyletic.
• Each supergroup has unique characteristics that set them apart from others.

Protist Super Groups

• Protist classification is based on morphological and DNA data, and is subject to revision as new information becomes available.

Exavates

• Exavates are characterized by a unique groove on one side of their cytoskeleton, giving them an "excavated" appearance.
• They have modified mitochondria and two major groups with flagella that differ from other organisms.

Diplo Monads

• Diplo monads are a subgroup of exavates with modified mitochondria called microsomes, which lack an electron transport chain.
• They generate energy through anaerobic pathways and have two nuclei and multiple flagella.
• Many diplo monads are parasites, and an example is Giardia lamblia, which causes severe diarrhea and vomiting in humans.

Parasitic Diplomonads

• Giardia lamblia is a parasite found in stagnant water that can infect animals, especially dogs.
• It has an excavated side, modified mitochondria, and multiple flagella.

Parabasalids

• Parabasalids are a subgroup of exavates with a reduced number of mitochondria called hydrogenosomes, which are anaerobic and produce hydrogen gas as a byproduct.
• An example is Trichomonas vaginalis, a sexually transmitted disease that causes burning and itching sensations in women.

Parabasalids Characteristics

• Trichomonas vaginalis eats the wall of the vaginal lining, causing symptoms.
• It has an excavated side, multiple flagella, and other key characteristics of exavates.

Euglenoids

• Euglenoids are a subgroup of exavates with a rod-shaped structure inside their flagella and a kinetic plastid, a large mitochondrion with a large amount of DNA.
• They are free-living parasites, and an example is Trypanosoma, which causes African sleeping sickness and Jacques disease.

Euglenoids Characteristics

• Trypanosoma affects red blood cells, causing fever, fatigue, and an enlarged appearance.
• It has an undulated membrane, flagella, and an excavated side.

Neuglenoids

• Neuglenoids are a subgroup of exavates with a pocket at one end, from which one or two flagella emerge.
• They are mixotrophic, meaning they can undergo photosynthesis or ingest other organisms to gain energy.
• An example is Euglena, a typical microscopic organism found in pond water.

Neuglenoids Characteristics

• Euglena has a long, oval shape with a curved, excavated side.
• It has a pocket at one end, from which its flagella emerge.

Brown Algae

• Multicellular organisms that resemble plants in structure and function
• Consist of a holdfast that anchors them to rocks or substrate, but does not absorb nutrients like plant roots
• Have a stipe that resembles a stem and blades that contain photosynthetic cells
• Some species have air bladders that help them float upright and reach the surface of the water for more light
• Exhibit an alternation of generations, with sporophyte and gametophyte generations
• Sporophyte generation is diploid, produces spores through meiosis
• Gametophyte generation is haploid, produces gametes (eggs and sperm)
• Sporophyte generation produces spores that develop into gametophytes, and gametophyte generation produces gametes that fertilize to produce a new sporophyte generation

Life Cycle of Brown Algae

• Begins with fertilization, where a sperm fertilizes an egg to produce a zygote
• Zygote undergoes mitosis to produce a sporophyte, which grows and develops into a mature organism
• Sporophyte produces spores through meiosis, which develop into gametophytes
• Gametophytes produce gametes, which fertilize to produce a new sporophyte generation

Characteristics of Brown Algae

• Belong to the group Stramenopiles, characterized by having two flagella, one smooth and one hairy
• Capable of producing spores used for reproduction

Red Algae

• Multicellular organisms with an abundance of phycoerythrin, giving them a red color
• Can vary in color due to presence of other pigments
• Some species are edible and used in foods like sushi
• Typically found in marine environments

Green Algae

• Multicellular organisms found in both freshwater and marine environments
• Majority of algae living in freshwater, often filamentous
• Some species are flagellated and have a spherical shape, such as Volvox
• Important contributors to the food chain, providing energy for organisms like fish, snails, and sea urchins

Amoeboid Protists

• Amoeboid protists are not a monophyletic group and are classified into two different groups: Rhizaria and Uniconta.
• Rhizaria protists have thin, slender extensions called pseudopodia, used for locomotion and capturing prey.

Rhizaria

• Radialaria and Foraminifera are subgroups of Rhizaria.
• Radialaria have tests made of silica, with intricate and beautiful patterns and shapes.
• They have thin, slender pseudopodia for locomotion and capturing prey.

Foraminifera

• Foraminifera have tests made of calcium carbonate, a mineral abundant in seawater.
• They have thin, slender pseudopodia for locomotion and capturing prey.
• Their tests have perforations, small openings for the pseudopodia to move out and extend.
• Some Foraminifera have endosymbiotic algae that help them obtain sugar through photosynthesis.

Uniconta

• Uniconta is a clade that includes protists, animals, and fungi.
• It includes amoeboid protists, such as slime molds, that are not closely related to other protists.

Slime Molds

• Slime molds are a type of amoeboid protist, also known as acellular slime molds.
• They are composed of many cells with no plasma membrane dividing the cells.
• They have a mesh-like network of cytoplasm and nuclei.
• They form a sporangium when conditions become unfavorable, which releases spores through meiosis.
• The spores germinate into haploid amoeba cells.

Cellular Slime Molds

• Cellular slime molds are a type of amoeboid protist, different from acellular slime molds.
• They are composed of individual cells, each with its own nucleus and plasma membrane.
• They form multicellular aggregates and eventually form a fruiting body that produces spores.
• The solitary amoebas that emerge from the spores can engage in sexual reproduction or make aggregates.

Other Amoeboid Protists

• Tubulinians (formerly known as Gemmyna) are a type of amoeboid protist that move using cytoplasmic streaming.
• They are heterotrophic and feed on other protists, algae, and bacteria.
• Entamoeba histolytica is a type of amoeba that causes gastrointestinal disease, including amoebic dysentery, a leading cause of death in humans worldwide.

Euglenozoa is a diverse clade consisting of euglenids and kinetoplastids, with distinct features such as spiral rods in flagella and kinetoplast DNA. They can be predatory, photosynthetic, or parasitic.