INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

PROTISTS - PROTISTA

PROTOZOA

SARCODINES

PHYLUM AMOEBOZOA

CLASS LOBOSEA

SUBCLASS TESTACEALOBOSIA

Predominantly freshwater and soil amoeboid organisms that move by means of lobopodia and secrete a single-chambered test (shell).

Structure. The test can vary in shape—spherical, flattened, pyriform, etc. It is composed of a keratin-like proteinaceous substance secreted by the ectoplasm. Sometimes the test is incrusted with sand grains (such as in the genus Difflugia), diatom frustules, etc., which the amoeba captures with its lobopodia and then deposits onto The surface of the test. In the common freshwater Arcella vulgaris, the test is saucer-shaped, with an opening on the underside known as the aperture (Mouth), through which the lobopodia emerge (Fig. 20). The amoeba does not completely fill the cavity of the test; instead, it is anchored within it by epipodia—cytoplasmic outgrowths attached to the inner wall of the test. Externally, The Cell is covered by a Plasma Membrane with a thin layer of glycocalyx. There may be one, two, or many nuclei, and one or two (rarely more) contractile vacuoles.

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Fig. 20. Testate amoebae (after Hausmann): Arcella vulgaris: a - ventral view; b - lateral view; c - Difflugia:

1 - test; 2 - Cytoplasm; 3 - nucleus; 4 - aperture; 5 - pseudopodia; 6 - digestive vacuole

Testate amoebae feed on Bacteria, Algae, fungal spores, Protozoans, and even rotifers, capturing them with their lobopodia.

Reproduction is asexual; during Cell Division, one of the daughter Cells remains in the parental test, while the other constructs a new test. A Sexual process in the form of autogamy—the fusion of nuclei within a single individual followed by the restoration of the binucleate state—has been documented only in Arcella vulgaris.

Testate amoebae inhabit Water bodies rich in organic matter (so-called eutrophic waters). Many species live in Sphagnum bogs and moist soils, contributing to pedogenesis (soil formation). Due to their high reproduction rates, they can reach remarkable densities—up to 800 million per 1 m²—with a biomass, despite their microscopic size, of up to 8 kg per 1 hectare.