Trivalvularis immunda

Trivalvularis immunda Siemensma and Dumack, 2019

Diagnosis: Shell spherical, organic, usually covered or encrusted with a number of mainly flat siliceous xenosomes of different size; color depending of aging process colorless to yellow and yellowish brown. Pseudostome triangular shaped, flexible, can be closed. In front of the pseudostome a hump of plasm is present from which filopodia and granulopodia radiate in all directions, unevenly branching and anastomosing, with extremely rapid bi-directional movement of granules, comparable with those of Arachnula. From main granulopodia smaller ones may branch at right angles. Between granulopodia very thin plasma threads may be present. It is remarkable that both filopodia and granulopodia are present (Filopodia lack any granules). Plasma body divided in an anterior part with some contractile vacuoles and a posterior part with granules, some of them resembling truncate bi-pyramidal crystals. Nucleus surrounded and obscured by the granules and crystals. Structure of the nucleus unknown. Cells are not very sensitive for light, they can be stationary for many hours, but also locomotive specimens have been observed. Stationary cells can collect a bunch of garbage around them.

Dimensions: Shell c. 23-28 µm (n=26)

Ecology: Fresh water, mesotrophic. In a pond of Crailoo (2014) and a ditch in Gaasterland (2016 and 2019) , both in the Netherlands and in stagnant rainwater along a country road on a hill slope near Hyères, Southern France (2014). Observed food: small algae, diatoms, Diplophrys sp..

Remarks: At first sight, the organism remembers Paralieberkuehnia elegantula, but its filopodial network shows more resemblance with that of Arachnula species, with extremely fast moving membranosomes and branching granulopodia at right angles. This network also resembles that of foraminifers, but without the whirling movement inside the shell as is characteristic for that taxon.

The pseudostome reminds a bit of the oral apparatus of Gromia oviformis as described by Hedley (1960).

Up to twenty specimens appeared in wet mounts kept in a moist chamber for some weeks. Observed specimens were attached to the cover slip or to the bottom.

Specimen with fully employed granofilopodia

Extremely thin hairlike filopodia, two are arrowed. I’m not sure if these fine threads belong to the amoeba.

Large granulopodia with smaller side-branches and in between some very thin hair-like filopodia.

Granulopodia with extremely thin hairlike filopodia in between. Detail of the image above.

Branching filopodia at right angles

Reconstruction and impression of the structure of the pseudostome

These three images were made at different levels, where the first is the lowest level and the third one the highest. It seems to be more than a simple triangular pseudostome, but it is difficult to imagine how this apparatus functions as a pseudostome, while it seems to be closed.