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Frenzelina

(Andersen, 1989; Schonborn, 1992; Bobrov et al., 1995; Foissner and Korganova, 1995; Wanner 1995, 1999). Verification of the validity of this test-centred taxonomy and whether it is useful at the genus or species level awaits phylogenic comparison of DNA sequences (Wanner et al., 1997). Additional characteristics such as mating types and conjugation, life history details, food preferences and optimal abiotic conditions for activity would be useful. One common culture limitation may be the absence of suitable test synthesis material or sensitivity to changes in the soil solution composition (or culture medium). In the Difflugina (Testacealobosea) with the test composed of cemented soil mineral particles, there could be variation in shape or size reflecting the availability of different mineral particles between soil types.

The reticulate genera are not usually sampled, and it is difficult to estimate their abundance in soils. Their feeding habits are diverse and they tend to be larger species up to 500 ^m in spread. The most common edaphic species are the Vampyrellidae, with numerous filopodia not usually anastomosing, and mitochondrion cristae that are best described as vesiculate. Cell divisions occur at the end of a feeding period in the cyst or at excystment. The best known in soils are the Arachnulla which can ingest bacteria and cysts, but are best known for puncturing fungal cell walls in hyphae and spores (Fig. 1.17). The Nucleariidae resemble vampyrellid amoebae with several ultrastructural differences. They have discoid-flat cristae with filose branching pseudopods. The pseudopods extend mostly from the sides of the cell and do not possess microtubular elements. Species feed on microdetri-tus or bacteria, or penetrate algal protists. Other reticulate genera include Biomyxa, Leptophrys (which feeds on algae and nematodes) and Theratromyxa (a multinucleate plasmodial genus which consumes nema-tode larvae and hyphae).

Fig. 1.17. Reticulate amoebae. (A) A vampyrellid amoeba (Vampyrellidae, Cercozoa). (B) A nuclearid amoeba, Theratromyxa (Nucleariidae, Cercozoa). Scale bar 50 ^m.

The Colpodellidae (probably should be in phylum Sporozoa) are tiny cytotrophic predacious species that resemble free-living Sporozoa (also called Apicomplexa by some authors). The rostrum ultrastructure resembles the tissue-invading organelle of the parasitic species. The cells attack eukaryotic cells by bumping into the cell membrane until the invasive organelle is triggered. They proceed to ingest the prey cytoplasm. They may also aggregate around dying or wounded microinver-tebrates along with other coprozoic species, such as the ciliate Coleps.

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