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Trinema complanatum
Trinema complanatum – courtesy of  © eye of science (www.eyeofscience.com)

Genus Trinema Dujardin, 1841

Diagnosis: test composed of two types of scales, large circular plates and smaller circular or broad elliptical plates in between or overlapping; aperture subterminal, ventral, circular or broad oval, invaginated, with rows of toothed apertural plates; apertural rim with oval small scales. Nucleus vesicular. Filopodia.

Ecology: very common in water, between mosses and in soil.

Remarks: species are very variable in size and shape and hard to identify.

Key to the species:

1 Aperture circular with a thin border; length of test less than twice the breadth   2
Aperture oval with a thick border; length of shell at least twice the breadth 4
2 Test small elliptical, length usually < 40 um T. lineare
Test broader, elliptical to ovoid; length usually > 45 µm 3
3 Test < 80 µm T. enchelys
Test > 100 µm T. grandis
4 Anterior end very compressed with a thick anterior lip; aperture slightly invaginated T. complanatum
Test in side view ovoid; aperture distinctly invaginated, with broad bend anterior lip T. penardi
Trinema penardi
Trinema complanatum
Trinema lineare
Trinema lineare
From Lueftenegger et al 1988
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