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Mayorella
Typical Mayorella shape

Genus Mayorella Schaeffer, 1926

Diagnosis: Locomotive digitiform subpseudopodia extending from anterior hyaloplasm; floating form often with long pseudopodia, radiating from an irregular body; nucleus usually spherical with a central nucleolus; most species with prominent cytoplasmic crystals, truncated, paired, bipyramidal or clustered with spheroids; cell surface as a cuticle, 200 nm thick.

Ecology: The genus is widespread in freshwater and marine habitats.

Type species: Mayorella bigemma (Schaeffer, 1918).

Remarks: This genus is morphologically identical with  Korotnevella (=Dactylamoeba). Only with TEM methods the surface cuticle of Mayorella can be distinguished from the surface microscales of Korotnevella.
The contractile vacuole, often more than one present, differs so far known from Korotnevella species by the way it empties. The contractile vacuole is replaced by hyaloplasm in Mayorella. According to Page (1988) this phenomenon appears to be one means of distinguishing between Mayorella and Korotnevella without using the electron microscope.
About 30 species have been described.

“The wide list of Mayorella-like amoebae species mentioned in the literature without detailed description indicates that light microscopy does not provide reliable data for identification of Mayorella species (Bovee 1985, Page 1988, see also Goodkov and Buryakov 1988 and Smirnov 1999). Transmission electron microscopy revealed a characteristic structure of cell coat (‘cuticle’) in Mayorella, which is a genus-specific character, but this finding did not solve the problem of species identification entirely because of the variability of cell coat structure under different fixation procedures (Page 1983, 1988). From the published data we can reasonably suggest that species diversity within the genus Mayorella is much higher than described presently, and
high molecular diversity of Mayorella-like amoebae recovered in the present study confirms this suggestion.”

(Cited from Glotova, Bondarenko and Smirnov, 2018)

Mayorella contractile vacuole
Mayorella contractile vacuole
Contractile vacuole of Mayorella: h = hyaloplasm; cv = shrinking contractile vacuole; o = original size of contractile vacuole. Right: the same contractile vacuole, some seconds later, now almost completely replaced by hyaloplasm.
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Mayorella
Mayorella
The drawings show some common species.
Mayorella
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