world of amoeboid organisms

Assulina muscorum
Assulina muscorum
Shell 47 and 55 µm, dry moss on roof and tree

Assulina muscorum  Greeff, 1888

Diagnosis: shell usually brown, ovoid, laterally flattened, biconvex in cross-section, with overlapping elliptical scales, usually arranged in alternating diagonal rows or occasionally irregularly; aperture narrow oval, more or less crenulate with margin of organic cement; the amount of cement around the aperture varies, but is often pronounced. Plasma colorless with a median band of granules. Nucleus vesicular. Numerous vacuoles usually present. Pseudopodia filose, seldom branched, straight, radiating, and few in number.

Dimensions: Length 33-60 µm (Hoogenraad and De Groot, 1940); 28-58 µm (Cash et al, 1915); 45-53 µm (Ogden & Hedley, 1980)

Ecology: mosses and Sphagnum, soil; very common. Cosmopolitan.

Remarks: Although empty tests are nearly everywhere numerous, living animals are not very common, and active individuals are rarely observed. In situations where moss is liable to considerable desiccation, individuals are few and their tests are often distorted; a large proportion of the empty tests are found with the two sides pressed together; this weakness may be due to the lenticular shape of the tests in transverse section (Cash et al, 1915).

Assulina muscorum
Assulina muscorum
In Sphagnum, Vosges, France 2019

Greeff found this species commonly in soil and dry mosses on rocks, walls and trees. He described it as much smaller than A. seminulum, and deep greyish brown. Pseudostomal edge with small sometimes curved teeth or irregularly in contour or sharply cut-off. Test compressed, spherical or ampul-shaped like A. seminulum. Greeff considered A. muscorum as a soil variety of A. seminulum.

Greeff 1889: „Außer der oben behandelten, an Assulina seminulum vorläufig anzuschliessenden Art, die ich bisher hauptsächlich in tieferen, an Feuchtigkeit und Humus mehr oder minder reichen Moosrasen im Walde fand, trifft man unter dünnen und dünnsten Flechten und Moosdecken auf Steinen, an Bäumen, Mauern etc. noch eine andere, viel kleinere, tief grau-braune Form, deren Gehäuse entweder gar keine oder eine sehr zarte, erst bei stärkerer Vergrößerung sich lösende hexagonale Sculptur erkennen lässt. Der Peristomrand ist entweder mit kleinen, zuweilen etwas gebogenen Zähnchen besetzt oder regelmäßig gezackt, wie bei Assulina seminulum oder endlich scharf abgeschnitten. Das Gehäuse hat, auf einer Breitseite gesehen, eine ähnliche sphäroide oder ampullenartige Gestalt wie A. seminulum. Ich glaube diese Form vorläufig als eine besondere Art oder eine Varietät von A. seminulum und zwar als die typische Land-Assulina ansehen zu müssen, da sie in den angegebenen Grössen- und Form-Verhältnissen überall in der Erde an der erwähnten Oertlichkeiten auftritt.“

Reference: Anderson, O. R. and Cowling, A. J.: The Fine Structure of the Euglyphid Testate Amoeba Assulina muscorum (Rhizopoda: Euglyphidae) with Observations of Growth Rate in Culture, Morphometries, and Siliceous Scale Deposition – Europ. J. Protistol. 30, 451 – 461 (1994)

Assulina muscorum
A. muscorum, 54 µm, stacked image
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