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The spirotrichs are a large and diverse group of ciliate protozoa. They typically have prominent oral cilia in the form of a series of polykinetids, called the adoral zone of membranelles, beginning anterior to the oral cavity and running down to the left side of the mouth. There may also be one or two paroral membranes on its right side. The body cilia are fused to form polykinetids called cirri in some, and are sparse to absent in others.
The heterotrichs are a class of ciliates. They typically have a prominent adoral zone of membranelles circling the mouth, used in locomotion and feeding, and shorter cilia on the rest of the body. Many species are highly contractile, and are typically compressed or conical in form. These include some of the largest protozoa, such as Stentor and Spirostomum, as well as many brightly pigmented forms, such as certain Blepharisma.
The peniculids are an order of ciliate protozoa, including the well-known Paramecium and related genera, such as Frontonia, Stokesia, Urocentrum and Lembadion. Most are relatively large, freshwater forms that feed by sweeping smaller organisms into the mouth. They have weird life cycles, and in many cases do not even form resting cysts.
The Litostomatea are a class of ciliates. The group consists of three subclasses: Haptoria, Trichostomatia and Rhynchostomatia. Haptoria includes mostly carnivorous forms such as Didinium, a species of which preys primarily on the ciliate Paramecium. Trichostomatia (trichostomes) are mostly endosymbionts in the digestive tracts of vertebrates. These include the species Balantidium coli, which is the only ciliate parasitic in humans. The group Rhynchostomatia includes two free-living orders previously included among the Haptoria, but now known to be genetically distinct from them, the Dileptida and the Tracheliida.
Extrusomes are membrane-bound structures in some eukaryotes which, under certain conditions, discharge their contents outside the cell. There are a variety of different types, probably not homologous, and serving various functions.
The hypotrichs are a group of ciliated protozoa, common in fresh water, salt water, soil and moss. Hypotrichs possess compound ciliary organelles called "cirri," which are made up of thick tufts of cilia, sparsely distributed on the ventral surface of the cell. The multiple fused cilia which form a cirrus function together as a unit, enabling the organism to crawl along solid substrates such as submerged debris or sediments. Hypotrichs typically possess a large oral aperture, bordered on one side by a wreath or collar of membranelles, forming an "adoral zone of membranelles," or AZM.
Blepharisma is a genus of unicellular ciliate protists found in fresh and salt water. The group includes about 40 accepted species, and many sub-varieties and strains. While species vary considerably in size and shape, most are easily identified by their red or pinkish color, which is caused by granules of the pigment blepharismin.
Holotricha is an order of ciliates. The classification has fallen from use as a formal taxon, but the terms "holotrich" and "holotrichous" are still applied descriptively to organisms with cilia of uniform length distributed evenly over the surface of the body.
Stylonychia is a genus of ciliates, in the subclass Hypotrichia. Species of Stylonychia are very common in fresh water and soil, and may be found on filamentous algae, surface films, and among particles of sediment. Like other Hypotrichs, Stylonychia has cilia grouped into membranelles alongside the mouth and cirri over the body. It is distinguished partly by long cirri at the posterior, usually a cluster of three. The largest can just be seen at a 25x magnification, and the smallest can just be seen at a 450x magnification.
A cytostome or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuoles. Only certain groups of protozoa, such as the Ciliophora and Excavata, have cytostomes. An example is Balantidium coli, a ciliate. In other protozoa, and in cells from multicellular organisms, phagocytosis takes place at any point on the cell or feeding takes place by absorption.
The oligotrichs are a group of ciliates, included among the spirotrichs. They have prominent oral cilia, which are arranged as a collar and lapel, in contrast to the choreotrichs where they form a complete circle. The body cilia are reduced to a girdle and ventral cilia. In Halteria and its relatives, they form bristles or cirri; however these forms may be closer relatives of the stichotrichs than of other oligotrichs. These organisms are very common in plankton communities, especially in marine systems. Usually found in concentrations of about 1 per ml, they are the most important herbivores in the sea, the first link in the food chain.
Vorticella is a genus of bell-shaped ciliates that have stalks to attach themselves to substrates. The stalks have contractile myonemes, allowing them to pull the cell body against substrates. The formation of the stalk happens after the free-swimming stage.
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different undulating pattern than flagella. Cilia occur in all members of the group and are variously used in swimming, crawling, attachment, feeding, and sensation.
Euplotes is a genus of ciliates in the subclass Euplotia. Species are widely distributed in marine and freshwater environments, as well as soil and moss. Most members of the genus are free-living, but two species have been recorded as commensal organisms in the digestive tracts of sea urchins.
The Apostomatida are an order of ciliates from the class Oligohymenophorea. Individual organisms from this the order are called apostomes. They are symbiotic with Crustacea. For majority of their life cycle they are dormant and encysted on their host's exoskeleton. The life cycle of apostomes varies; most genera will multiply through the biological process of fission causing the larvae to develop within the crustacean host. Physical characteristics may include a small cytostome (mouth), often accompanied by a glandular rosette and sparse hair like projections (cilia) arranged in spiral rows on the organism.
Intramacronucleata is a subphylum of ciliates. The group is characterized by the manner in which division of the macronucleus is accomplished during binary fission of the cell. In ciliates of this subphylum, division of the macronucleus is achieved by the action of microtubules which are assembled inside the macronucleus itself. This is in contrast to heterotrich ciliates of the subphylum Postciliodesmatophora, in which division of the macronucleus relies on microtubules formed outside the macronuclear envelope.
Glaucoma is a genus of freshwater ciliates in the Oligohymenophorea. Cells in this genus are between 30–150 µm long, and have three membranelles that surround the oral cavity. Two of the membranelles are used to sweep water towards the mouth, while the third acts like a sieve to strain out food particles for ingestion. In contrast, many other filter-feeding oligohymenophoreans use the paroral membrane, also known as an undulating membrane, for this purpose, but the paroral is not well-developed in Glaucoma.
Tracheloraphis is a genus of ciliates in the family Trachelocercidae.
Stentor roeselii is a free-living ciliate species of the genus Stentor, in the class Heterotrichea. It is a common and widespread protozoan, found throughout the world in freshwater ponds, lakes, rivers and ditches.
Halteria, sometimes referred to as the jumping oligotrich, is a genus of common planktonic ciliates that are found in many freshwater environments. Halteria are easy to locate due to their abundance and distinctive behaviour with observations of Halteria potentially dating back to the 17th century and the discovery of microorganisms. Over time more has been established about their morphology and behavior, which has led to many changes in terms of classification.
References
- ↑ Lynn, Denis. The Ciliated Protozoa. Springer, 2008. p. 31. ISBN 978-1-4020-8238-2 e- ISBN 978-1-4020-8239-9
- ↑ Kudo, Richard R. Protozoology. 4th ed. Charles C. Thomas, 1954. p. 59.
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