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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Trigonopyxis

Trigonopyxis Penard, 1912 (ref. ID; 3686)

Rhizopoda (ref. ID; 2032, 4863)

Order Arcellinida Kent, 1980 (ref. ID; 6790)

Centropyxidae Deflandre (ref. ID; 7501)

ref. ID; 1923

Hemispherical shell with foreign particles, without plate secreted by the cytoplasm. Aperture triangular. One species. (ref. ID; 1923)

ref. ID; 3686

Shell brown; circular or hemispherical; composed of agglutinated mineral particles; aperture central, invaginated and triangular. (ref. ID; 3686)
  1. Trigonopyxis arboricola Decloitre (ref. ID; 2522 original paper)
  2. Trigonopyxis arcula (ref. ID; 7076)
  3. Trigonopyxis arcula (Ehrenberg) Leidy (ref. ID; 2304, 2329, 2456)
  4. Trigonopyxis arcula (Leidy, 1879) (ref. ID; 3686, 6790) reported year? (ref. ID; 7857) or (Leidy, 1879) Penard, 1902 (ref. ID; 4737), (Leidy, 1879) Penard, 1912 (ref. ID; 661, 1618, 1923, 2032, 2077, 2146, 2189, 2238, 2362, 2408, 2441, 2489, 2862, 4755), (Leidy) Penard, 1912 (ref. ID; 5461) reported year? (ref. ID; 3283, 3595, 3598)
    See; Difflugia arcula (ref. ID; 2580)
    Syn; Cystidina arcula Van Oye (ref. ID; 2489); Difflugia arcula Leidy, 1879 (ref. ID; 1923); Difflugia arcula Penard (ref. ID; 2489); Trigonopyxis arcula Cash (ref. ID; 2489)
  5. Trigonopyxis arcula sensu lato Leidy, 1879 (ref. ID; 4863)
  6. Trigonopyxis arcula var. major Chardez, 1960 (ref. ID; 4863)
  7. Trigonopyxis foliumicola Chardez, 1976 (ref. ID; 2146)
  8. Trigonopyxis leidyi Couteaux & Chardez, 1981 (ref. ID; 2411 original paper)
  9. Trigonopyxis microstoma Hoogenraad & De Groot (ref. ID; 2110, 2456)
  10. Trigonopyxis minuta Schonborn, 1988 (ref. ID; 2032 original paper) reported author and year? (ref. ID; 4863)

Trigonopyxis arcula (Leidy, 1879) (ref. ID; 3686, 6790) reported year? (ref. ID; 7857) or (Leidy, 1879) Penard, 1902 (ref. ID; 4737), (Leidy, 1879) Penard, 1912 (ref. ID; 661, 1618, 1923, 2032, 2077, 2146, 2189, 2238, 2362, 2408, 2441, 2489, 2862, 4755), (Leidy) Penard, 1912 (ref. ID; 5461) reported year? (ref. ID; 3283, 3595, 3598)

See

Difflugia arcula (ref. ID; 2580)

Synonym

Cystidina arcula Van Oye (ref. ID; 2489); Difflugia arcula Leidy, 1879 (ref. ID; 1923); Difflugia arcula Penard (ref. ID; 2489); Trigonopyxis arcula Cash (ref. ID; 2489)

Descriptions

Test hemispherical, base slightly concave, but not invaginated; aperture triangular, central, trilobed; test yellowish with scattered sand-grains or diatoms; in sphagnous swamp, moss, soil. etc. (ref. ID; 1618)

Aperture triangular or irregularly trilobed, or roughly quadrangular, never invaginated. Habitat marshy places, among moss or Sphagnum. (ref. ID; 1923)

The shell is yellow or brown, circular, and hemispherical in lateral view. The apertural surface is smooth and slightly invaginated, the organic cement that covers the apertural surface extends over the rim of the shell, and the aboral surface is rough. The aperture is triangular, central and surrounded by a small collar. Specimens with irregular and quadrangular apertures are described by Cash et al., 1909. (ref. ID; 3686)

Shell brownish, hemispheric. Aperture central, clearly invaginated, in ideal case triangular, but often more or less irregular, surrounded by a small ring of organic cement. Cash & Hopkinson (1909) also describe great differences in the shape of the aperture. Nucleus with some spheric nucleoli. (ref. ID; 4755)

Shell composition is agglutinate; position of aperture is ventral. (ref. ID; 6790)

Measurements

Diameter 100-140 µm. (ref. ID; 1618)

Diameter 90-120 µm. (ref. ID; 1923)

Diameter of shell 95-168; depth of shell 58-88; diameter of aperture 21-42 µm (n=7). (ref. ID; 3686)

Shell dimensions (µm): diameter 90-168, depth 40-80, diameter of aperture 21-45. (ref. ID; 6790)

Trigonopyxis arcula sensu lato Leidy, 1879 (ref. ID; 4863)

Descriptions

The shell is circular, and occasionally broadly elliptic in apertural view. It is hemispherical in the lateral view. The pseudostome is positioned on the apertural (ventral) side and has a thickened lip around the periphery. It shape varies from being triangular, three-lobed, irregular to nearly circular. The edge of the pseudostome can be wavy to somewhat serrated. The colour of the shell can be yellowish-gold to dark brown, often becoming darker as the shell size increases. The shell is predominantly organic in composition containing scattered large organic and mineral particles (xenosomes) over the shell. These particles are usually more abundant on the dorsal side than on the ventral side. Smaller shells generally lack xenosomes. In order to test the differences between the populations, the Kolmogorov-Smirnov test was selected. It is a univariate test that has been shown to be sensitive to any differences between two populations (Campbell 1989). Results of testing suggest that differences between Siberian and Ontario populations in shell size and pseudostome diameter are statistically insignificant. However, according to the scatter diagram, the two populations do exhibit differences. In the Ontario population shell size and pseudostome diameter are tightly correlated (r=0.941); the smaller shells have smaller pseudostome diameters and the larger shells have larger pseudostome diameters. On the contrary, in the Siberan population such a relation is virtually lacking (r=0.033). This may indicate that the Ontario population is more homogeneous than the Siberian population. Another important observation is the degree of variability in the shape of the pseudostome in both populations. The edge of the pseudostome varies from being smooth, slightly wavy, to somewhat serrated. (ref. ID; 4863)

Trigonopyxis minuta Schonborn, 1988 (ref. ID; 2032 original paper) reported author and year? (ref. ID; 4863)

Diagnosis

Shell nearly hemispherical, height of shell averaging 65% of shell diameter. Aperture central, invaginated, only rarely triangular and rimmed, smaller than that of T. arucla, roughly circular to irregularly oblong. Colour brownish; xenosomes composed of plain stones and detritus particles like T. arcula. An internal shell exists and is (where the external shell is broken) clearly visible. (ref. ID; 2032)

Comments

T. minuta seems to have been found already by other authors. Bonnet (1977, Nepal; 1978, Jvory Coast), Couteaux (1972, 1975, Europe) and Couteaux & Munsch (1978, Guadeloupe) make reference to a Trigonopyxis arcula "petite forme". Couteaux & Munsch (1978) found two sizes of Trigonopyxis in the their samples, 70 µm and 100 µm diameter, in agreement with the population at Plothen. (ref. ID; 2032)

Type locality

Spruce foreset soil at Plothen (GDR, Thuringia). (ref. ID; 2032)

Measurements

Shell diameter 68.7-87.5 µm (average 76.3); shell height 43.7-56.2 (average 49.3) µm; aperture 12.5-21.9 long (average 17.1) µm. (ref. ID; 2032)