| DARK GROUND
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A type of imaging in microscopy in which the object appears bright against a dark background . It is achieved by illuminating the object obliquely. This is a micrograph of one of the Acantharea. [Link to this definition]
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| DAUGHTER COLONIES / DAUGHTER CELLS
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The products of cell division of protists. [Link to this definition]
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| DESICCATION
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Drying out. [Link to this definition]
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| DESMID
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A type of green alga of the family Desmidiaceae (Ralfs, 1848). [Link to this definition]
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| DESMODEXY, LAW OF
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The Law of Desmodexy, formulated by Chatton and Lwoff for ciliates,
states that an observer,within the organism, oriented like the organism and facing outward, would always see the kinetodesma on the right of an antero-posteriorly oriented kinety. In this example a portion of the ventral somatic infraciliature of Paramecium caudatum is viewed from outside the cell (anterior at top of image). The yellow arrowheads indicate individual kinetodesmata arising from kinetosomes and the blue arrowhead indicates the Kd fiber formed by the overlapping of individual kinetodesmal fibers. Silver carbonate.
[Link to this definition]
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| DESMOTHORACID
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A sessile protists in which a heliozoon-like organism is located within a lorica (e.g., Clathrulina, Fig. **). [Link to this definition]
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| DETRITOVORE
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Eats detritus. [Link to this definition]
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| DETRITUS
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Fragments of dead plant and animal material before, during and after breakdown by agents of decay. May incorporate inorganic matter (such as mud). [Link to this definition]
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| DIAGNOSTIC
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Used in relation to a particular character (feature) of an organism which is quite distinctive and therefore can be used to identify that organism. [Link to this definition]
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| DIATOM
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A kind of protist with chloroplasts and a siliceous lorica/wall. Of two kinds, centric and pennate. Common and widespread. [Link to this definition]
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| Diatotepum
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A distinct, continuous organic layer found between the siliceous frustule and the plasma membrane in diatoms. Previously referred to as the “pektin” or “diatopectin” layer, this terminology was confusing due to the possible chemical interpretations. The diatotepum stains for acidic polysaccharide and has been described for a number of diatoms, mostly centric. The diatotepum is considered a distinct layer (= “diatotepic layer”) in addition to the organic coat (= organic casing). The latter envelopes the surface of all siliceous components of the frustule. [Link to this definition]
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| DICHOTOMOUS
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A pattern of branching in colonial organisms in which one element (talk) gives rise to two equal and divergent branches. Also used in reference to identification keys in which the identity of an organism is established by presenting questions for which there are only two acceptable answers. [Link to this definition]
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| DICHOTOMOUS KEY
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PATHWAY KEY [Link to this definition]
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| DIFFERENTIAL INTERFERENCE CONTRAST:
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A type of imaging used in light-microscopy in which boundaries of refractive index difference are revealed as a light/dark boundary (Fig. **). Ideal for the study of protists as a very thin optical slice is taken through the specimen so that organelles are shown clearly (= Nomarski). [Link to this definition]
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| DIFFERENTIATION
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The act of becoming specialized (differentiated) in form or function. Protists may be specialized to feed (theronts), to weather unfavourable conditions (cysts) or hunt out new resources (theronts) - each of these states is achieved through differentiation. [Link to this definition]
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| DIFFUSION FEEDING
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Feeding strategy which the predator relies on the movements of the prey to make contact - as in heliozoa and suctoria. [Link to this definition]
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| Digital
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[Link to this definition]
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| DIPLOMONAD
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A type of flagellate (Fig. **) with two nuclei and two sets of four flagella, e.g. Trepomonas, Hexamita. [Link to this definition]
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| Discharge plug
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Gelatinous, highly refractive material secreted between the plasma membrane and sporangial wall at early stages of spore formation in chytrids. Found among diverse chytrids including those with operculate and inoperculate zoospore discharge. [Link to this definition]
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| Discharge vesicle
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Extracellular material produced during zoosporogenesis in fungal and algal protists, which at spore or protoplast discharge, evaginates into an external sac, constraining spores until they rupture the vesicle. Involved in zoospore discharge of many algae and oomycetes such as Pythium and chytridiomycetes such as Chytriomyces. Also appropriately applied to the polaroplast of Microsporidia. See also, Gun cell. [Link to this definition]
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| DISPERSED
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Said of bacteria which float freely or swim in a fluid environment (in contrast to attached or adhering). [Link to this definition]
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| Dissecting scope
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A microscope with relative low magnifying powers but with a very wide field of view and with a long working distance between the object and the objective lenses. Suitable for low power scanning of samples. Also referred to as binocular microscope. [Link to this definition]
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| DISTAL
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Away from (contrast with proximal). [Link to this definition]
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| DIVISION
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The most common mechanism of reproduction of protists, in which a cell replicates itself by dividing in two - the plane of division of ciliates is usually across the cell body (transverse); flagellates usually divide longitudinally. [Link to this definition]
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| Dormant basal body/kinetosome
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Nonflagellate/nonciliate, fully formed with a full complement of triplet microtubules, eventually giving rise to a flagellum/cilium. These occur in many flagellate green algae (e.g., Chlamydomonas, Pedinomonas), in some euglenophytes, in some chromophytes. If the developmental status of a basal body/kinetosome that is not associated with a flagellum/cilium is unknown, it should simply be referred to as nonflagellate/nonciliate. Synonyms: non-functional basal body, non-functional kinetosome. [Link to this definition]
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| DORSAL
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Refers to the back of the cell, the face of the cell away from the ventral (see ventral). The concept does not always apply. [Link to this definition]
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