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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 2043

Harald Netzel; [The Ultrastructure of the Test in Difflugia oviformis (Rhizopoda, Testacea)]. Arch.Protistenk.Bd. 118:321-339, 1976

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In Difflugia oviformis the wall of the test consists of a single layer of siliceous idiosomes (polymorphous particles made within the cell) and organic cement in the interstices. The idiosomes, smooth and rounded in outline and surface, are considerably variable in size (between 1 and 161 in groundplan area). They are randomly arranged, their long axis or broader face being parallel to the surface. In general, the idiosomes are juxtaposed, although in some cases there may be slight marginal imbrications. Outer and inner face of the wall are similar in appearance. The joints (interstices) are filled -mostly without a gap- by an organic cement with complex structure and polar orientation. The cement generally dose not adhere to the outer and inner face of the idiosomes, respectively. Only at the collar-like margin of the test aperture the idiosomes may be wholly surrounded by cement. The units of the cement appear to be bi-concave elliptical discs with thickened margin, about 1 µm in diameter. In broad joints the discs are arranged parallel to the surface. A system of cavities within the discs is perpendicular to a "ground plate", which is oriented towards the interior of the cell. In narrow joints the units may be in an oblique or even vertical position. The discs are interpreted to be directed from bilaterally symmetrical "thecagenous granules". These granules are about 0.5-0.7 µm in size. Their fine structure is complex. An electrondense matrix includes a system of cavities, very similar to that visible in the cement units (granular-cement-hypothesis). About 2,500-6,000 idiosomes are incorporated into one shell, glued together by between 5,000 and 58,000 transformed granules. The surface area of the joints is between 11% and 30% of the total surface area of the shell. Granular cement seemingly also occurs in other species of Difflugia and in the genera Lesquereusia and Nebela.