Genus Lacogromia Siemensma et al., 2017
Diagnosis: Test elongated to broadly pyriform or lens- or spindle-shaped, with a layer of small siliceous xenosomes and usually with some organic particles of debris. Test colorless or yellowish to almost black; aperture straight or oblique; test up to 1000 µm long. Usually with 1-8 nuclei, sometimes up to 30. Nuclei spherical, ovular.
Type species: Lacogromia cassipara
Lacogromia squamosa (Penard, 1899)
Lacogromia brunneri (Blanc, 1886)
Lacogromia palustris (Thomas, 1961)
Morphological variations: Siemensma et al. (2017) found morphological differences between populations from different locations and consider them as different morphotypes (A and B). Cells of type A look grayish or brownish grey when observed under transmitted light. The colour depends on the kind of food in the cytoplasm, the number of crystal-like particles and the colour of the agglutinated material in the test wall. Mineral material is commonly colourless, but organic particles are mostly ochre yellow, brown or black. Tests of type B vary in colour, those of younger, smaller specimens are light ochre yellow, and tests of older, larger spec-imens are darker ochre yellow or reddish brown and black. The colour is not always evenly distributed. Usually the proximal and apertural region are darker. Another difference between the two types is the covering of the proximal part. Tests of morphotype B have an extra layer of loosely attached particles, resembling a kind of cap, while tests of morphotype A do not have any extra covering. Agglutinated particles of these caps are larger than the regular ones, up to 10 µm. The length of all observed tests, both alive or empty, varied between 91 and 560 µm (mean 264 µm, std. dev. 77, n=333), with a width of 48–407 µm (mean 154 µm). The average length/breadth ratio is 1.8, with extremes between 1.1 and 3.5. Biometrical analysis showed differences in this ratio between both morphotypes (Graph below). Differences between both morphotypes are summarized inthe table below.
|L. cassipara||Morphotype A (n=224)||Morphotype B (n=109)|
|Aperture||No pronounced collar, smooth||Distinct collar with double ring, often with constriction|
|Shape||Broadly ovoid-pyriform, proximal end broadly rounded||Elongated ovoid - elongated pyriform, or spindle-shaped; proximal end conical, rounded|
|Proximal end||Without extra cap of particles||Usually with cap of larger particles|
|Structure||Particles loosely attached||Particles close to each other|
|Colour||Colourless or light ocre yellow||Dark brown, ocre yellow or black|
|L/B ratio||1.1–2.4, mean 1.5||1.7–3.5, mean 2.3|
|Length||91–530 µm, mean 262 µm||123–560 µm, mean 267 µm|
|Width||48–407 µm, mean 173 µm||46–202 µm, mean 117 µm|
|Nuclei, diameter||18–66 µm, mean 38.6 µm||8.7–77 µm, mean 29.0 µm|
Reference: Ferry Siemensma, Laure Apothéloz-Perret-Gentil, Maria Holzmann, Steffen Clauss, Eckhard Völcker, Jan Pawlowski: Taxonomic revision of freshwater foraminifera with the description of two new agglutinated species and genera, European Journal of Protistology 60 (2017) 28–44.
Penardogromia palustris Thomas 1961
According to Thomas (1961), the test is covered with calcareous particles, but we doubt if this is specific to this species and therefore a distinctive feature. In fact, Siemensma et al. 2017 find the description of P. palustris insufficient to distinguish it from other related species. Though Thomas described the test as elongated tubular, he did not mention anything about the flexibility, extensibility and pliability of the test, which is so characteristic for tubular species. Based on the original drawing (Thomas 1961) the species resembles much more a small Lacogromia than a Limnogromia species. The test in this drawing (Thomas 1961) also resembles the deviating specimen in slide 433 of the Penard Collection.