Trinema grandis (Chardez, 1960) Golemansky, 1963
Diagnosis: Shell ovoid, elongate and hyaline; ventral side in the same plane as the aperture, while the dorsal surface is convex and bulges; test composed of two types of scales: one type large, the other type small, covering the space between the large scales. Aperture oval or circular, sub-terminal and invaginated, bordered by an inner circle of denticulate apertural-plates.
Dimensions: Chardez (1960): Shell length 110—115 um long. My measurements: up to 155 µm (Ecuador), 117—124 µm (n=2) (Mongolia, 2024).
Habitat: In mosses.
Geographical distribution: Cosmopolitan.
Remarks: During a search for Trinema enchelys shells in material from a Mongolian fen (Łuców et al., 2024), I found some shells that were much larger than normal but otherwise identical. In one sample, I discovered a shell 92 µm long, whereas all other shells ranged from 44–67 µm in length. In another sample, I found only a few shells, measuring 57–95 µm, with lengths more or less evenly distributed.
In two additional samples, I observed two large specimens, measuring 117 and 124 µm in length. The large scales on these specimens had diameters of 13.5—14.2 µm, and the small scales were approximately 5.6 µm long. These two very large Trinema shells could represent T. grandis (Chardez, 1960) Golemansky, 1963, although this species is described as having smaller scales (according to Chardez’s Fig. 14). The specimens illustrated by Golemansky (1963) differ from those described by Chardez in having a flattened anterior part.
Interestingly, Chardez (1960) noted that these ‘giants’ never form large populations, although Golemansky (1963) reported a ‘rich population.’ The large shells in both KH samples were, apart from their size, completely similar and comparable to the ‘normal’ population of T. enchelys. The giant forms had scales twice as large as the regular specimens, and their lengths were also approximately double. Remarkably, there were no transitional forms between the regular and giant specimens.
Giant forms have also been recorded for Arcella formosa by Siemensma (2024). Similarly, Dallimore et al. (2000) reported tests that were significantly larger than typically observed, including ‘giant’ specimens 2–3 times larger. They suggested this could reflect low ambient temperatures and a short growing season.
