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glossary
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| TARDIGRADES
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A type of cute little metazoa, with an exoskeleton and eight stubby legs ending in claws and an exoskeleton. [Link to this definition]
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| TAXONOMY
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That area of biology which relates to naming and classifying organisms (more or less = systematics). [Link to this definition]
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| Test
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A hardened cell covering, forming a partial or complete enclosure, typically secreted by the organism or built up of particles gathered from the environment, forming a protective barrier around the cell; often used as a general descriptive term for a wide variety of hard-coverings, loricae, shells, thecae, or valves . The term “test” lacks much specificity in its typical usages being applied to diverse enclosures including those of diatoms, testate amoebae, and some monothalamic foraminifera. In general, a test may be defined more restrictively as a relatively thin-walled enclosure that almost fully surrounds the cell, with one or only a few major openings; this is distinguished from a shell that is thick-walled and may have many pores and openings, or a lorica that more loosely encloses the cell and has few to many openings. [Link to this definition]
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| TESTATE
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Bearing a test. [Link to this definition]
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| Theca
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Term used in various connections throughout protist taxa to describe a wall-like structure. The theca of dinoflagellates is composed of thecal plates, each lodged in a vesicle [amphiesmal vesicle ] located inside the plasma membrane. In diatom frustules , the valve together with the girdle elements (cingulum) associated with it is called the “theca”. In the prasinophytes Tetraselmis and Scherffelia, the theca is an extracellular more or less close-fitting membrane surrounding the cell. It is composed of fused organic scales. In the choanoflagellates, members of the Salpingoecidae are surrounded by a theca, an extracellular usually close-fitting membrane, which may be extended into an anterior collar and posterior stalk. Epitheca is the anterior part of the theca in dinoflagellates (the area of the cell in front of the cingulum or girdle), the hypotheca is the posterior part of the theca. In diatoms, the older valve and its associated elements is called “epitheca”, the hypotheca is the newer part of the theca. Testate amoebae, enclosed in an organic or mineralized shell , are sometimes referred to as thecate amoebae. See Lorica, Test. [Link to this definition]
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| thecal
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Term describing the plasma membrane and the underlying flattened vesicles of dinoflagellates (amphiesmal vesicles = thecal vesicles) which in some species contain plates (= thecal plates). In certain naked dinoflagellates the amphiesmal vesicles appear to be without plate-like structures. Apparently the same system of vesicles underneath the plasma membrane occurs in ciliates, some apicomplexans, glaucophytes, and perhaps other protists (see Alveoli), but the term amphiesma is presently restricted to dinoflagellates. [Link to this definition]
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| THERONT
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A form adopted by some species of ciliates that typically does not feed but moves quickly. May be thought of as an adaptation in response to a lack of food and the task of which is to hunt out new sources of food. [Link to this definition]
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| TIF
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A format for digital images, said to be lossless - in that the quality of colours and resolution in the image is preserved when editing and saving. TIF images require a lot of memory. In preparing digital images for web pages, all early editing should be done using the TIF format to preserve quality. However, final images should be saved in jpg format if they are photographs, or GIF if they are drawings. Both types of image require less memory, but there is a degradation in quality. This is illustrated in the picture. A pair of parallel lines with a colour gradient were drawn, saved using the different file formats, and then magnifed 10 times. The tif images show slight loss of sharpness but retain the tonal range and colour quality; gif images retain sharpness but the tonal range is converted into a series of steps; and the jpg image shows tonal range but considerable degradation of colour quality. [Link to this definition]
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| TRAILING
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[Link to this definition]
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| Transitional fibers
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Thin strands extending from a point between the A- and B-tubules to the plasma and flagellar membranes, beginning where the axoneme assumes the 9 + 2 arrangement and ending where the distal ends of the C-tubules terminate. In the flagellum/cilium, the transitional fibers are short and extend straight to the membrane. Below the transitional region they are necessarily longer and sometimes are whorled like a Catherine wheel. In chytrids the transitional fibers below the transitional region are especially large, often with secondary fibers. Synonyms: accessory spokes, anchoring fibers, curving arms, kinetosome props, links, props, struts. [Link to this definition]
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| Transitional helix
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A thick helix (or possibly stacked rings) that lies inside the outer doublets of the axoneme but apparently does not connect with them. This type occurs in many but not all chromophyte algae and Oomycete fungi. A "double helix" occurs in some Oomycetes, hyphochytriomycetes, bicosoecids, slopalinds, and the xanthophyte Heterococcus. The "coiled fiber" of the green alga Pyramimonas may belong in this category. Synonyms: coiled fiber, Spiralkorper. [Link to this definition]
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| Transitional plate
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Thin, plate-like structure oriented perpendicularly to the axoneme, usually filling the lumen of the axoneme and sometimes extending to the flagellar membrane. The transitional plate can vary significantly in its location, number and detailed structure. Synonyms: axosome, basal plate, terminal cap, terminal partition, terminal plate, transverse diaphragm, transverse septum. [Link to this definition]
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| Transitional region/transitional zone
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The most proximal (basal) part of a flagellum/cilium adjacent to the basal body/kinetosome; comprising matrix, axoneme, and flagellar/ciliary membrane. Comments: The transitional region is sometimes defined as the region between the proximal ends of the central pair of microtubules of the axoneme and the distal ends of the C-tubules of the basal body/kinetosome. However, we prefer a more general definition because some transitional structures cross over these boundaries. For example, the transitional helix of chromophytes and the helix of the euglenids Entosiphon extend into the region containing the central pair of microtubules of the axoneme. The transitional region may include three major components: (1) concentric fibers, (2) transitional plate, and (3) transitional fibers. It must be emphasized here that we do not imply a homology among taxa; we are only identifying positional and structural similarities. Synonyms: transition region, transition zone, flagellar transition region. [Link to this definition]
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| TRICHOCYST
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A type of extrusome which, when extruded, takes the form of a fine stiff filament. Typical of Paramecium, but used inadvertently to refer to other types of extrusomes. [Link to this definition]
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| Tripartite hairs
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Filamentous appendages consisting of a tapered base, a cylindrical shaft and one or more terminal filaments; characteristic of many chromophyte algae, Oomycete fungi and some heterotrophic flagellates. The shaft bears long and short filaments in several groups but lacks filaments in others; hairs are usually arranged in two rows along the length of the flagellum and attached through the flagellar membrane to specific outer doublets. [Link to this definition]
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| TROPHIC
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Said of organisms which are active and feeding, and contrasts with the encysted state, theronts, or swarmers. May also be used to refer to those aspects of metabolism associated with growth. [Link to this definition]
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| TROPHONT
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The feeding stage of an organism. For heterotrophic protists, this is most of the life. Alternative stages are theront (rare), swarmers, and cysts [Link to this definition]
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| Tubular flagellar hairs
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Filamentous appendages consisting of at least a hollow shaft (> 15 nm diam.) often with one or more terminal filaments. Tubular hairs are of three major types: bipartite hairs, tripartite hairs, and hair-scales. Bipartite and tripartite hairs are first assembled in the (chloroplast) endoplasmic reticulum or nuclear envelope while hair-scales are assembled in the Golgi apparatus; the former are composed principally of glycoproteins and the latter are of complex carbohydrates. Synonyms: mastigoneme. [Link to this definition]
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| TYPE
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In nomenclature, an object that serves as the fixed reference point for the name of a taxon. For species and infraspecific taxa (e.g. subspecies, variety), the type is usually a specimen; the type (most precisely, the HOLOTYPE) of the species Ulva lactuca is a specimen identified by Linnaeus and conserved in the herbarium at Lund, Sweden. For taxa of higher rank, the type is the name of a taxon at the next lower rank; for the order Ulotrichales, the type is the family Ulotrichaceae. [Link to this definition]
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