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Difflugia angustata
Difflugia angustata, Gaasterland, 2019

Difflugia angustata  (Deflandre, 1926) comb. nov.
Basionym: Difflugia angustata  (Penard, 1890) Deflandre, 1926

Diagnosis: This species differs from d. elegans by its more slender pace and its smaller size and the commonly curved spine. The width is proportionately smaller, the mouth remaining substantially similar; nucleus with a limited number of nucleoli; nucleoli with small lacunae.

Dimensions: Deflandre (1926): Length (ex. icon.) 70 µm; Length/Width ratio 2.52 to 2.71. Ogden (1984): Length 95–118 μm, Width 44–51 μm, aperture diameter 24–27 μm (n=4). My measurements: Length 61-96 µm (n=20); nuclear diameter 14.3 µm (n=1).

Remarks: I found this species together with a population of the typical D. elegans in Gaasterland, 2019. The distinction between both groups was clear. Therefore I consider it as a separate species. According to Ogden (1984), the only features that differentiate this variety from the type are the elongate shape of the shell and the absence of a constriction near the aperture.

Ecology and distribution: Freshwater. Venezuela (Deflandre, 1926), Serbia (Ogden, 1984), Netherlands.

Original description (Deflandre, 1926): “Malgré de notables variations de la forme chez D. elegans je crois néanmoins bon de distinguer comme variété une série d’individus que j’ai trouvés plusieurs fois, suffisamment semblables entre eux pour admettre une certaine fixité: var. angustata var. nov. (Penard, 1902 page 247, fig. 11). La variété diffère du type par son allure plus élancée. La largeur est proportionnellement plus faible, la bouche restant sensiblement semblable. Le rapport de la longueur à la largeur qui, dans les formes typiques varie entre 1,54 et 1,77, atteint ici de 2,52 à 2,71 (fig. 10)
Distribution. Mare Mangas Goberas, Venezuela.” (Translated: Despite notable variations in form in D. elegans, I nevertheless believe it is good to distinguish as a variety a series of individuals that I have found several times, sufficiently similar to each other to admit a certain fixity: var. angustata var. nov.. The variety differs from the type by its more slender appearance. The width is proportionately smaller, the mouth remaining substantially similar. The ratio of the length to the width which, in typical forms varies between 1.54 and 1.77, reaches here from 2.52 to 2.71 (fig. 10)).

Difflugia elegans angustata
D. elegans var. angustata, a after Penard, 1902; b after Deflandre, 1926; c after Ogden, 1984
Difflugia angustata
D. angustata, all shells descended from one specimen which multiplied in a moist-chamber-mount, 79-86 µm long – Naardermeer, 2016.
Difflugia elegans - Ferry Siemensma
D. angustata, all shells from the same culture as above, 83-96 µm long – Naardermeer, the Netherlands
Difflugia elegans angustata
D. angustata, Gaasterland
Difflugia elegans angustata
D. angustata, nucleus
Difflugia bicornis
D. angustata; plot of a number of measurements of shells from the Gaasterland location, July 2019. It might be possible that D. bicornis falls within the variation of D. elegans, though the latter has smaller tests, but D. angustata seems a distinct species and not just a variety.

Difflugia elegans var. angustata Deflandre 1926 changed to Difflugia angustata (Deflandre, 1926)
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 15, 2019; last modified January 31, 2022
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