| RAPHE
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A slit along the flat faces of the siliceous shell of most pennate diatoms. Those diatoms which are motile always have a raphe, and it appears to be involved in the secretion of mucus that pushes the cell around. [Link to this definition]
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| RAPTORIAL
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A type of feeding in which the comsumer moves around in search of suitable nourishment (compare diffusion or suspension feeding). [Link to this definition]
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| RECURRENT FLAGELLUM
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A flagellum which curves posteriorly from its site of insertion, to trail along the body and/or behind the body. [Link to this definition]
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| REDUCED
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A chemical state of some environments in which free oxygen is absent and if made available will be chemically consumed by the molecules present. Typically a site rich in sulphides (such as hydrogen sulphide) and methane, usually black in colour and with a strong smell. Also used in reference to some parts of cells to indicate small size or absence (reduced flagella are short). [Link to this definition]
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| REFRACTILE
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Capable of refracting light, thereby acting like an irregular lens. Refractile granules may appear bright when viewed with a microscope, but may also be a source of chromatic aberration, appearing coloured when they are not. [Link to this definition]
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| RESERVOIR
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A part of euglenid cells, a depression from which the flagella arise and into which the contractile vacuole empties its contents. Also referred to as a flagellar pocket. [Link to this definition]
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| RESOLUTION - DIGITAL
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[Link to this definition]
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| RESOLUTION - MICROSCOPY
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[Link to this definition]
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| RHIZOPODA
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Those amoebae which have pseudopodia with no stiffening axoneme (STEP **). [Link to this definition]
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| RIDGE
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Slightly raised elongate region of a structure [Link to this definition]
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| RIMOPORTULA
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Plural: rimoportulae. Hollow tubular process in the valve of centric diatoms, through which polysaccharides and other carbon-containing substances are extruded. Characterized by a lip-shaped aperture on the internal face of the valve. Synonym: labiate process. Image provided by Charley O'Kelly. [Link to this definition]
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| ROTIFER
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A type of metazoan animal, also called a wheel animal because of the two clusters of motile cilia around the mouth. [Link to this definition]
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| RUMEN
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[Link to this definition]
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| RUMINANT
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The term ruminant refers usually to a type of herbivorous mammal. As mammals do not have enzymes to digest plant cell walls, they rely on microbial communities to do this. In the case of ruminents, they have a large chanber in the gut which acts as a digestion chamber. This is the rumen and contains vast numbers of bacteria, fungi and protozoa. Cattle and related organisms - such as buffalo - are ruminents. Some other vertebrates and invertebrates also have digestion chambers in their guts and sometimes these too are referred to as ruminants. [Link to this definition]
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