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glossary
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| Labeling of doublets/triplets
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The axonemal doublets can be labeled in some protists using either a bridge that may occur between doublets 5 and 6 or the missing dynein arm on doublet 1 (many green algae). Doublets are numbered sequentially in an anti-clockwise pattern when the flagellum is viewed from tip to base. Once the doublets are labeled, they can be followed into the cell and the triplets can be numbered accordingly. [Link to this definition]
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| Labeling of flagellar roots
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To date, labeling of flagellar roots has been the most variable of all the cytoskeletal structures. Names have been descriptive (e.g., SRm, 4 r, Cr, 12 r in Chilomonas) or arbitrary (e.g., Rl, R2, R3, etc. in Poterioochromonas). Before the discovery of flagellar transformation, flagellar labeling was arbitrary in distantly related taxa. As a consequence, root homologies were difficult to establish. However, with consistent flagellar labeling (see above), it is possible to have consistent labeling of roots; it remains uncertain whether consistency in position and structure means homology. [Link to this definition]
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| Labeling of flagellum/cilium and basal body/kinetosome
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Many flagellate/ciliate protists bear two flagella/cilia per cell (ciliates being an obvious exception); these two must be distinguished. This has been done with a variety of names in the individual groups: dorsal/ventral, anterior/posterior, hairy/smooth, left/right, short/long, cis/trans. The problem is to compare a specific flagellum/cilium between groups, or specifically, to establish homologies. Recent studies on flagellar/ciliary development have added a new dimension to this problem. During cell division, the flagella have a semi-conservative replication such that each daughter cell receives an existing flagellum and each forms a new one. The newly formed flagella are termed immature, and during the following cell division they transform to a more mature state. The developmental process spans at least two cell cycles before a flagellum is fully mature; it remains mature for all subsequent cell divisions. This flagellar/ciliary heterogeneity and the recognitions of flagellar transformation have led to a new means for identifying and labeling flagella/cilia and their basal bodies/kinetosomes. The oldest flagellum is Number 1, the next oldest is Number 2, etc. A uniflagellate cell may have either a Number 1 or a Number 2 flagellum, while a biflagellate cell will have both Number 1 and Number 2 flagella. [Link to this definition]
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| LABIATE PROCESS
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See rimoportulae [Link to this definition]
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| Lacuna
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see
Alveoli.[Link to this definition]
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| LAMP HOUSING
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Part of a microscope containing the lamp. Now built into the body of compound microscopes, but previously a free-standing structure - and still is for some dissecting microscopes. Older microscopes used mirrors to direct the light from independent lamps, candles, or the sun into the microscope. This microscope has two lamps, the lower one used to project light through a specimen, the upper one used to project light onto the specimen from above. [Link to this definition]
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| LARGE
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A relative measure of size, the exact meaning of which depends on the range encountered in the group of organisms under consideration. Bodonids are motsly less than 10 microns long and a cell measuring 20 microns would be thought large, whereas, among the ciliates, a cell measuring 20 microns would be regarded as small and a ciliate would need to be well in excess of 100 microns before being thought of as large. Usually, protists with one dimension greater than 50 - 100 microns are usually referred to as large. [Link to this definition]
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| LENS TISSUE
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A special kind of tissue recommended for cleaning glass surfaces in microscopes and other optical instruments. Available from opticians and chemists as well as from laboratory suppliers. Use each sheet once and discard. [Link to this definition]
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| Lepidosome
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Epicortical,organic structures of definite shape produced intracellularly by trophicand/or cystic ciliate species.The term excludes unstructured mucus coats and any kind of lorica.This example shows typ I and type VI lepidosomes of Luporinophrys micelae (Foissner,2005). [Link to this definition]
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| LIP
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A shallow ledge or long protrusion from a cell, a widened margin, such as around the mouth of Stephanopogon. [Link to this definition]
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| LOBOSE
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A type of pseudopodium, relatively broad and rounded at the tip - such as these pseudopodia of Difflugia [Link to this definition]
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| LONGITUDINAL
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Relating to the axis of the cell from the front to the posterior of the cell. The groove on the surface of Notosolenus ostium is longitudinal, the axis of the cell being defined by the direction in which the cell moves (the flagellum is directed to the anterior) [Link to this definition]
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| LORICA
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A structure surrounding or enveloping the body of some ciliates and flagellates; it fits loosely over the body proper of the organism, with a wide opening at one, occasionally both end(s), and is sometimes attached to a substrate at the other pole (see Holdfast organelle). In tintinnid oligotrichs and flagellated protists it is often carried about by the organism freely swimming in the water column. Its composition may be of a calcareous, chitinous, pseudochitinous, proteinaceous, siliceous, or tectinous nature, or it may be mineralized by iron and manganese compounds, or it may be made up of sand grains, coccoliths, diatom frustules, or simply debris held together by a secreted “glue”. Broadly speaking, the following terms are sometimes synonymized with “lorica”: basket, case, envelope, house, sheath, shell, test, theca, tube, valve. Loricae are secreted or assembled by their occupants; when not solitary, they may appear in an arboroid “colony” arrangement. When an occupant has undergone cellular division during asexual reproduction in the lorica, one of the filial organisms often departs to secrete its own house elsewhere, the other remaining, often attached, in the parental abode. Peritrichs, folliculinids, and tintinnines are the major ciliate taxa in which loricae are to be found. As for flagellated protists, loricae occur in some choanoflagellates (acanthoecids), some (fossil) ebriids, euglenoid flagellates (e.g., Trachelomonas), chlorophytes (e.g., Phacotus) and heterokonts (e.g., Bicosoeca, Dinobryon, Epipyxis). Epipyxis produces a lorica composed of imbricate plates or scales of fibrillar construction. The loricae of acanthoecid choanoflagellates are uniquely basket-like, composed of costal strips (see Costa, Skeleton). A fine membranous or fibrillar investment (“lorica membrane”) lines part of these basketlike loricae and an extension of this attaches to the protoplast, holding it firmly in position within the lorica. The lorica of fossil ebriids is an inflated chamber-like structure which generally develops at the anterior end of the skeleton . In this example of Trachelomonas, the cell has been compressed b y the coverslip and the lorica has split open. [Link to this definition]
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| Lumen
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The central region of the basal body/kinetosome within the cylinder of nine triplet tubules. In the proximal part of the basal body/kinetosome the lumen is filled by the cartwheel. The lumen may appear "empty" or it may contain various inclusions such as ribosome-like particles, dense spheres, dense bodies, fibrils and amorphous clumps. [Link to this definition]
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