Centropyxis oblonga
C. oblonga, after Deflandre, 1929

Centropyxis oblonga  Deflandre, 1929  *)
Basionym: Centropyxis aculeata var. oblonga Deflandre, 1929

Diagnosis: In ventral view, the shell is oblong—elliptical or oval—but never circular. The aperture is proportionally larger, consistently elliptical, and often highly eccentric. In lateral view, the shell exhibits a high dome, taller than that of the type specimen. The spines vary in length and number but are always positioned at the posterior end. The shell’s integument is similar to that of the type, being punctuated to varying degrees of coarseness, with a coating of foreign materials and a few stones apposed near the posterior part.

Dimensions: Deflandre (1929): Shell length without spines 106-140 µm; width 95-111 µm. Bhutan population (2024): Length without spines: 145-224 µm; width 121-187 µm. Odenwald (2024): Length without spines

Habitat: Freshwater. Probably cosmopolitan.

Remarks: The diagnosis above was first provided by Deflandre (1929). I found specimens in a sample from the Odenwald, a large forested area in central Germany, that matched his description. However, smaller specimens had rounder shells. Morphometric analyses showed no evidence that these represented a different genus. A distinctive feature shared by all these shells was the presence of relatively large mineral particles on the anterior lip, along with a kind of beaded string of smaller mineral particles surrounding the aperture. The smaller shells closely resemble C. aculeata var. minima described by Van Oye (1938). Van Oye noted that this variety is half the size of C. aculeata, consistent with the smaller shells in the Odenwald population. While he did not explicitly mention it, his drawing depicts the characteristic large particles on the upper lip.

Centropyxis oblonga
In a population from Odenwald, Germany (2024), the largest C. oblonga shells were distinctly oblong.
Centropyxis oblonga
In the same Odenwald population, smaller C. oblonga shells tended to be more rounded than the larger ones.
Centropyxis oblonga
Centropyxis oblonga
C. oblonga, Bhutan, 2023
Centropyxis oblonga
Centropyxis oblonga
C. oblonga, Bhutan, 2023
Centropyxis oblonga
C. oblonga, Bhutan, 2023

*) Centropyxis aculeata var. oblonga Deflandre, 1929 changed to Centropyxis oblonga Deflandre, 1929.
Note: A formal change is not required in this case according to the International Code of Zoological Nomenclature: (1) According to article 45.6.3, as the name was published before 1961 using the abbreviation var., it is deemed to be subspecific rather than infra-subspecific and therefore falls under rulings for species-group nominal taxa (Chapter 10). (2) According to article 46.1, names established at either species ranks (species or subspecies) are simultaneously established at the other rank, with same author and same type. Authority thus is unchanged.
Ferry Siemensma, created August 24, 2023; last modified December 28, 2024
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