What type of protist are radiolarians

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We would like to thank Dr Ian Probert for insightful comments and English proof reading. This article is contribution number 50 of Tara Oceans. The 's with the advent of the Deep Sea Drilling Program saw another burst of research.

During the 's W. Riedel showed how Radiolaria evolved rapidly and could therefore be utilised as biostratigraphic tools. First recorded occurrences of Radiolaria are from the latest Pre-Cambrian, they are generally thought to have been restricted to shallow water habitats. By the Silurian deep water forms are believed to have evolved. All early Radiolaria are spumellarians, the first possible nassellarians appear in the Carboniferous and definite true nassellarians do not appear until the Triassic.

During the late Palaeozoic Radiolaria show a gradual decline until the end of the Jurassic when there is a rapid diversification, this coincides with the diversification of the dinoflagellates which may have represented an increased source of food for the Radiolaria.

It is thought that the evolution of diatoms in the Cretaceous may have had a significant effect on radiolarian evolution due to competition for silica diatoms also use silica to build their skeleton ; it is commonly accepted that radiolarian skeletons have become finer and less robust from this time. Extant radiolaria are classified using features of both the preservable skeleton and the soft parts, which makes the classificaiton of fossil forms extremely difficult.

Most workers in this field today use classification schemes based on Nigrini and Moore's and Nigrini and Lombari's works on modern and Miocene radiolarians. A major problem with radiolarian classification is that separate classifications have been established for the Palaeozoic, Mesozoic and Cenozoic, and little has been done to integrate them. The two suborders, the spumellarians and the nassellarians are subdivided into informal groups which equate to family level.

Radiolarian assemblages often contain species so they can potentially be very useful biostratigraphic and palaeoenvironmental tools. They have an unusually long geological range, from latest Pre-Cambrian to Recent. Because Radiolaria have a skeleton composed of silica and have an extremely long geological range they have become useful in the study of sediments which lack calcareous fossils, either because of deposition below the CCD Carbonate Compensation Depth or because the strata being examined are too old.

Cherts and particularly nodules within chert bands are often good sources for Radiolaria. Ophiolites and accretionary terrains often include chert bands and Radiolaria may be the only palaeontological aid available in these situations and as such have proved invaluable in the study of these geological settings.

Despite being single-celled protozoans Radiolaria are quite complex, sophisticated organisms. Movement of these two perpendicular flagella causes a spinning motion. Some dinoflagellates generate light, called bioluminescence, when they are jarred or stressed. Large numbers of marine dinoflagellates billions or trillions of cells per wave can emit light and cause an entire breaking wave to twinkle or take on a brilliant blue color. For approximately 20 species of marine dinoflagellates, population explosions called blooms during the summer months can tint the ocean with a muddy red color.

This phenomenon is called a red tide and results from the abundant red pigments present in dinoflagellate plastids. In large quantities, these dinoflagellate species secrete an asphyxiating toxin that can kill fish, birds, and marine mammals. Red tides can be massively detrimental to commercial fisheries; humans who consume these protists may become poisoned. Bioluminescence : Bioluminescence is emitted from dinoflagellates in a breaking wave, as seen from the New Jersey coast.

The apicomplexan protists are so named because their microtubules, fibrin, and vacuoles are asymmetrically distributed at one end of the cell in a structure called an apical complex.

The apical complex is specialized for entry and infection of host cells. Indeed, all apicomplexans are parasitic. This group includes the genus Plasmodium , which causes malaria in humans. Apicomplexan life cycles are complex, involving multiple hosts and stages of sexual and asexual reproduction. Parasitic apicomplexans : a Apicomplexans are parasitic protists.

They have a characteristic apical complex that enables them to infect host cells. The ciliates, which include Paramecium and Tetrahymena , are a group of protists 10 to 3, micrometers in length that are covered in rows, tufts, or spirals of tiny cilia. By beating their cilia synchronously or in waves, ciliates can coordinate directed movements and ingest food particles.

Certain ciliates have fused cilia-based structures that function like paddles, funnels, or fins. Ciliates also are surrounded by a pellicle, providing protection without compromising agility. The genus Paramecium includes protists that have organized their cilia into a plate-like primitive mouth called an oral groove, which is used to capture and digest bacteria. Food captured in the oral groove enters a food vacuole where it combines with digestive enzymes.

Waste particles are expelled by an exocytic vesicle that fuses at a specific region on the cell membrane: the anal pore. In addition to a vacuole-based digestive system, Paramecium also uses contractile vacuoles: osmoregulatory vesicles that fill with water as it enters the cell by osmosis and then contract to squeeze water from the cell.

Paramecium : Paramecium has a primitive mouth called an oral groove to ingest food and an anal pore to excrete it. Contractile vacuoles allow the organism to excrete excess water. Cilia enable the organism to move. Paramecium has two nuclei, a macronucleus and a micronucleus, in each cell.

The micronucleus is essential for sexual reproduction, whereas the macronucleus directs asexual binary fission and all other biological functions. The process of sexual reproduction in Paramecium underscores the importance of the micronucleus to these protists. Paramecium and most other ciliates reproduce sexually by conjugation. This process begins when two different mating types of Paramecium make physical contact and join with a cytoplasmic bridge.

The diploid micronucleus in each cell then undergoes meiosis to produce four haploid micronuclei. Three of these degenerate in each cell, leaving one micronucleus that then undergoes mitosis, generating two haploid micronuclei. The cells each exchange one of these haploid nuclei and move away from each other. A similar process occurs in bacteria that have plasmids.

Fusion of the haploid micronuclei generates a completely novel diploid pre-micronucleus in each conjugative cell. This pre-micronucleus undergoes three rounds of mitosis to produce eight copies, while the original macronucleus disintegrates.

Four of the eight pre-micronuclei become full-fledged micronuclei, whereas the other four perform multiple rounds of DNA replication and then become new macronuclei.

Two cell divisions then yield four new paramecia from each original conjugative cell. Paramecium : sexual reproduction : The complex process of sexual reproduction in Paramecium creates eight daughter cells from two original cells. Each cell has a macronucleus and a micronucleus. During sexual reproduction, the macronucleus dissolves and is replaced by a micronucleus.

Stramenophiles include photosynthetic marine algae and heterotrophic protists such as diatoms, brown and golden algae, and oomycetes. Describe characteristics of the following Stramenophiles: diatoms, brown algae, golden algae, and oomycetes.

Current evidence suggests that chromalveolates have an ancestor which resulted from a secondary endosymbiotic event. The species which fall under the classification of chromalveolates have evolved from a common ancestor that engulfed a photosynthetic red algal cell. This red algal cell had previously evolved chloroplasts from an endosymbiotic relationship with a photosynthetic prokaryote. Chromalveolates include very important photosynthetic organisms, such as diatoms, brown algae, and significant disease agents in animals and plants.

The chromalveolates can be subdivided into alveolates and stramenopiles. A subgroup of chromalveolates, the stramenopiles, also referred to as heterokonts, includes photosynthetic marine algae and heterotrophic protists. Many stramenopiles also have an additional flagellum that lacks hair-like projections.

Members of this subgroup range in size from single-celled diatoms to the massive and multicellular kelp. Stramenophile structure : This stramenopile cell has a single hairy flagellum and a secondary smooth flagellum. The diatoms are unicellular photosynthetic protists that encase themselves in intricately patterned, glassy cell walls composed of silicon dioxide in a matrix of organic particles.

These protists are a component of freshwater and marine plankton. Most species of diatoms reproduce asexually, although some instances of sexual reproduction and sporulation also exist. Some diatoms exhibit a slit in their silica shell called a raphe. By expelling a stream of mucopolysaccharides from the raphe, the diatom can attach to surfaces or propel itself in one direction. Diatoms : Assorted diatoms, visualized here using light microscopy, live among annual sea ice in McMurdo Sound, Antarctica.

During periods of nutrient availability, diatom populations bloom to numbers greater than can be consumed by aquatic organisms. The excess diatoms die and sink to the sea floor where they are not easily reached by saprobes that feed on dead organisms. As a result, the carbon dioxide that the diatoms had consumed and incorporated into their cells during photosynthesis is not returned to the atmosphere.

The biological carbon pump is a crucial component of the carbon cycle that helps to maintain lower atmospheric carbon dioxide levels. Like diatoms, golden algae are largely unicellular, although some species can form large colonies. Their characteristic gold color results from their extensive use of carotenoids, a group of photosynthetic pigments that are generally yellow or orange in color.

Golden algae are found in both freshwater and marine environments, where they form a major part of the plankton community. The brown algae are primarily marine, multicellular organisms that are known colloquially as seaweeds.

Giant kelps are a type of brown algae. Some brown algae have evolved specialized tissues that resemble terrestrial plants, with root-like holdfasts, stem-like stipes, and leaf-like blades that are capable of photosynthesis. The stipes of giant kelps are enormous, extending in some cases for 60 meters. A variety of algal life cycles exists, but the most complex is alternation of generations in which both haploid and diploid stages involve multicellularity.

For instance, compare this life cycle to that of humans. In humans, haploid gametes produced by meiosis sperm and egg combine in fertilization to generate a diploid zygote that undergoes many rounds of mitosis to produce a multicellular embryo and then a fetus.

However, the individual sperm and egg themselves never become multicellular beings. In the brown algae genus Laminaria , haploid spores develop into multicellular gametophytes, which produce haploid gametes that combine to produce diploid organisms that then become multicellular organisms with a different structure from the haploid form.

Terrestrial plants also have evolved alternation of generations. Brown algae life cycle : Several species of brown algae, such as the Laminaria shown here, have evolved life cycles in which both the haploid gametophyte and diploid sporophyte forms are multicellular. The gametophyte is different in structure from the sporophyte. The oomycetes are characterized by a cellulose-based cell wall and an extensive network of filaments that allow for nutrient uptake. As diploid spores, many oomycetes have two oppositely-directed flagella one hairy and one smooth for locomotion.

The oomycetes are non-photosynthetic and include many saprobes and parasites. The saprobes appear as white fluffy growths on dead organisms. Most oomycetes are aquatic, but some parasitize terrestrial plants. One plant pathogen is Phytophthora infestans , the causative agent of late blight of potatoes, such as occurred in the nineteenth century Irish potato famine. Rhizaria are a supergroup of protists, typically amoebas, that are characterized by the presence of needle-like pseudopodia.

The Rhizaria supergroup includes many of the amoebas, most of which have threadlike or needle-like pseudopodia. Pseudopodia function to trap and engulf food particles and to direct movement in rhizarian protists.

These pseudopods project outward from anywhere on the cell surface and can anchor to a substrate. The protist then transports its cytoplasm into the pseudopod, thereby moving the entire cell.