Microworld

world of amoeboid organisms

Menu
Microgromia
Microgromia
Microgromia haeckeliana, arrow indicates septum, 16.9 µm

Genus Microgromia Hertwig, 1874

Diagnosis: Shell hyaline, small, retort-shaped, double-sided symmetrically, sometimes with one side fastened to the substrate; outline circular, sometimes irregular or angular, with or without a distinct neck. The neck is curved and partially fused with the shell surface, thus forming an internal septum with a lateral aperture. Shell composed of an organic material without any embedded xenosomes; color usually yellow-brown till dark-brown. Cytoplasm with an asymmetrical or symmetrical bundle of filopodia which are granular (extrusomes), very thin, and are able to branch and anastomose, thus forming a network or reticulum. Nucleus relatively large, globular with a central nucleolus. One contractile vacuole.

Ecology: freshwater and marine; shallow, iron rich water; in mucous colonies of cyanobacteria.

Remarks: Recently Martin Kreutz published an excellent paper on this interesting but poorly known testacean group (Mikrokosmos, Heft 3, 2012), the first report after the publication of De Saedeleer (Beitrag zur Kenntnis der Rhizopoden, 1934). Kreutz notices the difficulty of identification species using the descriptions and drawings of De Saedeleer. Nevertheless he succeeded in the identification of five species in a pond in Simmelried, near Konstanz, Germany.
An important diagnostic characteristic is the presence or absence of an internal septum. However, because of the small dimensions of the scales, this characteristic is sometimes hard to observe under normal lightmicroscopical conditions. An 100X oil-immersion objective maybe very helpful to resolve fine details. It is curious that De Saedeleer based his description of a new species, Microgromia hertwigia, on the potential presence of a septum, which he never could observe!
According to De Saedeleer a septum can be oriented from left to right or vica versa. But this characteristic isn’t very useful if an observer can’t see if he is looking at a specimen in dorsal or ventral view (Kreutz, 2012).
De Saedeleer attaches great value to the visibility of the granular filopodia to identify species, but in my opinion this is not a useful characteristic.

Based on the observations of De Saedeleer and Kreutz, I propose the following key:

Shell nearly spherical, with a distinct, often thickened neck. Septum clear, usually with a shorter kind of septum at the base of the neck, thus forming a V-shape. Cytoplasm asymmetrical. M. longisaepimen
Shell nearly spherical, often angular, with a distinct neck and a rather curved but well developed septum. Cytoplasm asymmetrical. M. haeckeliana
Shell nearly spherical, without neck, with a very small aperture. Septum short. Cytoplasm nearly symmetrical. M. parvisaepimen
Shell spherical, somewhat elongated, with a distinct neck. Cytoplasm asymmetrical.

M. minor

Microgromia spec.
Microgromia
Microgromia spec., 13.6 µm, pseudopodial network about 200 µm large – Austria, Sphagnum
Microgromia spec BB
Microgromia spec. 13 µm – Bert Bospad
Microgromia longisaepimen
Microgromia spec., with pseudopodial network (granuloreticulum)
Microgromia longisaepimen
Microgromia spec., with extended pseudopodial network (granuloreticulum)
Recent posts

Centropyxis tropica

C. tropica, after Deflandre, 1929 Centropyxis tropica  Deflandre, 1929 Basionym: Centropyxis aculeata var. tropica Deflandre, 1929 Diagnosis: As for C. aculeata, but with much longer

Read More »

Centropyxis nauwercki

Centropyxis nauwercki, after Schönborn, 1975 Centropyxis nauwercki  Schönborn, 1975 Diagnosis: Shell divided by a ring groove into a highly convex, balloon-shaped fundus part and a

Read More »

Centropyxis pontifera

Centropyxis pontifera, after Bartos, 1963 Centropyxis pontifera  Bartos, 1963 Diagnosis: Test large, broadly oval, formed of a thick, solid, brownish-yellow organic matter. Test with many

Read More »

Centropyxis pyriformis

Centropyxis pyriformis, after Van Oye, 1958 Centropyxis pyriformis  Van Oye, 1958 Diagnosis: This species is distinguished from C. aculeata by its narrowed shape towards the

Read More »

Centropyxis dentistoma

Centropyxis dentistoma, after Decloitre, 1949 Centropyxis dentistoma  Decloitre, 1949 Basionym: Centropyxis aculeata var. dentistoma Decloitre, 1949 Diagnosis: Pseudostome lobed, with 4 to 7 sharp teeth,

Read More »

Centropyxis compressa

Centropyxis compressa, after Van Oye, 1948 Centropyxis compressa  Van Oye, 1948 Diagnosis: Test a little elongated and very flattened regularly, like that of Arcella discoides;

Read More »

Centropyxis lata

Centropyxis lata, after Jung, 1942 Centropyxis lata  Jung, 1942 Diagnosis: Shell coarse-scaled, covered with a mix of diatoms and detritus; pseudostome large, ventral side mostly

Read More »

Centropyxis aurita

Centropyxis aurita, after Laminger, 1973 Centropyxis aurita  Laminger, 1973 Diagnosis: In ventral view, the shell is more or less broadly ovoid in outline. Quite straight truncated

Read More »

Centropyxis grelli

Centropyxis grelli, after Laminger, 1973 Centropyxis grelli  Laminger, 1973 Diagnosis: Shell covered with relatively large mineral particles. The pseudostome outline is formed by two convex arches.

Read More »

Centropyxis adami

Centropyxis adami, after Laminger, 1971 Centropyxis adami  Laminger, 1971 Diagnosis: In ventral view, the outline of the shell is more or less elliptical, in side

Read More »