Actinocoma ramosa
Actinocoma ramosa

Actinocoma ramosa Penard, 1903

Diagnosis: Body naked, grayish, spherical or star-shaped, without a clear distinction between ectoplasm and endoplasm; surface with one or several large contractile vacuoles; cytoplasm containing small vacuoles and colorless brilliant grains. In the center of the plasm is a nucleus of unusually large size, very clearly drawn, with a very thick membrane, and filled with a nuclear juice with usually one nucleolus; sometimes two nucleoli are present.Nucleolus more or less spherical, normally with one or more small lacunae.
Pseudopodia radiating in all directions, rarely less numerous, most often in considerable numbers, straight and simple, or each branched into a certain number of filaments that deviate little from each other, thus taking together the appearance of a broom. These filaments bear mobile granules, very small and few in number (Original diagnosis, translated from French).

Dimensions: Penard (1903), central body 14-26 µm, my measurements: 22-31 µm. Nucleus 12-16 µm.

Ecology: Fresh water. In oligotrophic and mesotrophic watertypes, e.g. the Spiegelplas, a deep and large lake, and in the IJsselmeer near Kornwerderzand and in Crailoo, a mesotrophic pond, both in the Netherlands. It multiplied in wet mounts kept in humidity chambers. This species has also been found in the USA by Yana Eglit (2012, pers. comm.) and in Germany in a fresh water aquarium by Eckhard Voelcker (2015, pers. comm).

Remarks: The granules are very hard to detect, only with phase contrast they become more distinct. They are more numerous than Penard describes and they move in a bidirectional way. I have found this species several times. They came up in so called wet-chamber-mounts. The pseudopodia of my specimens differ from the ones described by Penard, but their nucleus fits well to his description. It is not unusual that amoeboids develop completely different pseudopodia when settled or attached to the slide. I have seen this phenomenon also with specimens of Clathrella foreli and Leptophrys-species.
Actinocoma ramosa is very sensitive to light. It reacts immediately when it comes within the light path of the microscope. It retracts its long pseudopodia and broad veils. What remains is a more or less spherical body with rod-like short pseudopodia moving and waving restlessly.
Penard (1903): “This curious body has the appearance of a heliozoaire, and would remind somewhat Actinophrys sol; by its branched pseudopodia and devoid of any axial filaments, it is an amoeboid rhizopod. It is still rare, and I found only a few individuals, at Point à la Bise, along the shore of the lake.”

Nucleus with two nucleoli. All specimens in a sample from Crailoo showed this phenomenon.
Actinocoma ramosa
Actinocoma ramosa, just some seconds after coming into the light beam of the microscope. Note the veils.
Actinocoma ramosa
Actinocoma ramosa, with relatively large ovoid nucleus and central nucleolus.
Actinocoma ramosa, with short and long pseudopodia. The short pseudopodia move continuously like waving sticks.
Actinocoma ramosa
Actinocoma ramosa
Actinocoma ramosa
Actinocoma ramosa
Actinocoma ramosa
Actinocoma ramosa
Actinocoma ramosa
Pseudopodium with granules (arrow) in bi-directional movement.
Actinocoma ramosa
Actinocoma ramosa
Actinocoma ramosa
Actinocoma ramosa, after Penard, 1903
Actinocoma ramosa
The same specimen as above.
Actinocoma ramosa
Actinocoma ramosa
Nucleus, 16 µm. Note the small vacuoles.
Actinocoma ramosa
Actinocoma ramosa, drawing: Ferry Siemensma (1981)
Actinocoma ramosa
Actinocoma ramosa, dividing
Actinocoma ramosa
Actinocoma ramosa, the same specimens as above.
Actinocoma ramosa
Actinocoma ramosa, nucleus
Actinocoma ramosa
Actinocoma ramosa, Spiegelplas
actinocoma ramosa - Ferry Siemensma
Actinocoma ramosa - Ferry Siemensma
Small specimen with two nucleoli
Recent posts

Sphaerothecina

Infraorder Sphaerothecina Kosakyan et al., 2016   Diagnosis: Testate amoebae with a more or less spherical or semi-spherical test and a central aperture; test build

Read More »

Microcorycia bryophila

after Decloitre, 1974 Microcorycia bryophila Decloitre, 1974 Diagnosis: “This species bears a slight remembrance to Microcorycia tessellata Penard. The differences are as follows: With tessellata,

Read More »

Pseudodifflugia procera

Pseudodifflugia procera, after Badewitz, 2003 Pseudodifflugia procera Badewitz, 2003 Diagnosis: Test elongated cylindrical, remarkably slim, with straight or slightly curved flanks, in cross-section circular. Living

Read More »

Christinellula spec.

“Christinellula” “Christinellula“ from Spiegelplas Diagnosis: This specimen was present in a sample from the Spiegelplas (‘Mirror Lake’) in the Netherlands. It differs from previous observed

Read More »

Thecamoeba sp. 3

Thecamoeba sp. n = nucleus Thecamoeba sp. Diagnosis: Surface in locomotion with some longitudinal dorsal folds; outline in locomotion broadly oblong; hyaloplasm usually in a

Read More »

Schoenbornia humicola

Schoenbornia humicola – after Schönborn et al., 1987 Schoenbornia humicola (Schönborn, 1964) Diagnosis: Test small, not compressed, hyaline, with Nebela-like irregular siliceous plates and sometimes

Read More »