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Ditrema longicollis
Ditrema longicollis.with central nucleus

Ditrema longicollis (De Saedeleer, 1934) new combination

Basionym: Diplophrys longicollis De Saedeleer, 1934

Diagnosis: Shell composed of organic material, shaped like a half dome or an iglo; shell wall without any xenosomes, hyaline; young cells colorless, older cells pale yellow and later yellow brown; young shells are circular, older cells more irregular in shape. Shell with two opposite pseudostomes, each with a clear cylindrical neck, hence the name longicollis. Protoplast doesn’t fill the shell fully, cell sometimes with epipodia connected to the shell. Periphery with up to twelve contractile vacuoles of different size. Granofilopodia present, usually three to five on each side. One pseudopodium runs straight out of each neck and branches into three to five granofilopodia, often at right angles. Filopodial granules clearly visible, but not evenly spaced; can differ strongly in density; spacing often at intervals between 5-12 µm. Cell and filopodia remain in contact with substrate or biofilm; immotile and solitary. Nucleus centrally, spherical with more or less irregular central nucleolus, sometimes surrounded by some small granules.

Dimensions: De Saedeleer: shell diameter without both pseudostomes 18.7-25.5 µm (n=23); neck 1.7-3.4 µm. My measurements: shell diameter without pseudostomes: 19.3-21.3 µm (n=6); neck 4.2-4.4 µm long; nucleus 4.9-6.8 µm, nucleolus 1.7-2.4 µm.

Ecology: feeds on small algae and probably bacteria. Fresh water. I found specimens in the biofilm on the surface of a fresh water pond. Belgium and the Netherlands.

Remarks: De Saedeleer considered this species to be a Diplophrys species and described it as Diplophrys longicollis (1934), but with that genus it has nothing in common, besides the two pseudostomes. The shell is half domed and seems to be double-layered.

Ditrema longicollis
Nucleus (l) and original drawing from De Saedeleer, 1934
Ditrema longicollis
Ditrema longicollis
Nucleus; the same cell in phase contrast
Ditrema longicollis
Older shell
Ditrema longicollis
Young cell with relatively large distance between the granules. The Netherlands.
Ditrema longicollis
Compare the distance between the granules with those in the specimen above. Specimen from a small stream in Bretagne, France.
Ditrema longicollis
Older shell. Notice the hyaline plasma spheres on the filopodia.
Ditrema longicollis
Ditrema longicollis with central nucleus
Ditrema longicollis
Ditrema longicollis, with characteristic T-shaped filopodia; notice the double layered shell wall (S)
Ditrema longicollis
Ditrema longicollis, p = pseudostome, n = nucleus, v = vacuoles
Ditrema longicollis
In phase contrast the double wall is clearly visible
Ditrema longicollis
Ditrema longicollis
Cell with green food particles
Ditrema longicollis
Ditrema longicollis
Ditrema longicollis
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