Difflugina

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Family Netzeliidae

Shell is ovoid, circular in cross-section, aperture is lobed, with a thick organic rim or a necklace made of small idiosomes. Shell is covered by idiosomes, although small sand grains, diatoms or undigested algal cell walls can be used as supplementary building material. These xenosomes are always smoothed and modified by the deposition of silica (Anderson, 1987). The idiosomes often have a nail-like shape. All particles are held in position by perforated cement units and are arranged in a single layer. Outline usually regular, but some species often have protuberances to give a mulberry-like appearance. Recently some spherical Difflugia (D. oviformis, D. tuberculata, D. wailesi, D. tricuspis, D. geospherica, etc.) that had been found able to produce endogeneous siliceous elements are expected to be removed from Difflugia, which is generally incapable to build shell without xenosomes (Ogden, 1979; Gomaa et al., 2017). Type genus: Netzelia Ogden, 1979.

Family Cucurbitellidae

Shell is ovoid, circular in cross-section, with distinct apertural collar, dark grey or opaque in color, with regular outline, covered by small to medium mineral grains. Organic cement seldom visible as surface structure. Aperture is terminal, with 3 to 12 lobes, composed of small mineral grains. Collar forms a cavity (frontal camera) which has an inner aperture (circular or lobed) on the level with the main body wall. Nuclear is vesicular, cytoplasm of some species contains zoochlorellae. Type genus: Cucurbitella Penard, 1902.

Family Centropyxidae

Bilaterally symmetrical shell, with an eccentric elliptic or circular aperture located on the ventral side; shell with xenosomes.

Family Distomatopyxidae

Shell is circular or ovoid in frontal view, hemispheric in lateral view. Aperture is central, elliptical, invaginated and lying at the bottom of a tubular vestibule. The vestibule is partly covered by a diaphragm which is fixed by two bridges forming two crescent-shaped openings at opposite sites. Shell is covered with xenosomes.

Family Hyalospheniidae

Shell is rigid, colourless or yellowish-brown, flask-vase shaped, oval or pyriform (can be circular or elongated), generally compressed, rarely circular in cross section (e.g. Longinebela golemanski, Padaungiella nebeloides). The shell is either entirely self-secreted composed of an organic matrix, or with addition of self-secreted siliceous plates or recycled shell plates of euglyphids, Quadrulella or other similar material such as diatom frustules incorporated in the shell. Aperture is terminal and is bordered by a more or less thin organic lip (rim, collar or fringe). Currently, family includes thirteen genera.

Family Lamtopyxidae

Shell is circular in frontal view; ventral surface is flat, dorsal surface is hemispheric. External aperture is bordered by large teeth, internal opening at the end of deeply invaginated tube, elliptic. Shell is covered with xenosomes.

Family Plagiopyxidae

Shell is bilaterally symmetrical; aperture is on ventral side, eccentric, cryptostome. Shell is covered by xenosomes.

Family Paraquadrulidae

Shells are composed of endogenously formed rectangular calcite plates embedded in a sheet-like organic cement. The presence of calcite still should be verified.

Family Trigonopyxidae

Shell is radially symmetrical, circular in outline; composed of sheet-like proteinaceoius matrix with agglutinated particles; aperture central.

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