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 complanatum
Trinema lineare
From Lueftenegger et al 1988