Paramphitrema muelleri Kiss and Török, 2009
Diagnosis: Paramphitrema with tubular or lemon-like fusiform rigid test, which is circular in cross section; test tapers towards the rigid apertures; nucleus vesicular; besides thin filopodia, 1-2 thick, straight, unbranched, tubular pseudopodia are also produced.
Dimensions: length of the test is about 13-17 µm.
Ecology: This species is rare. The description is based on 3 living specimens. Type locality: The plankton of the main arm of the River Danube at Göd, 20 km north from Budapest, Hungary.
Remarks: The shape of the test may be lemon-like, with a wide convex middle region, or tube-like with parallel sides. The test is composed of a thick, conspicuous, refractile, colorless or yellowish organic inner layer, which is covered by xenosomes, which are mineral quartz particles, the larger ones of which are usually flat plates. There is a quite regular pattern of dark circular holes and separating ribs among the xenosomes in the organic layer (the holes are about 0.2-0.3 µm diameter). In some specimens, a thick, irregularly arranged xenosome-covering is present near the apertures. The apertures are rigid, oval and slightly irregular, their diameter is 1-1.6 µm: longitudinal optical cross sections. A delicate organic rim may be present at the ends of the apertures.
The cytoplasm fills the test nearly entirely. It extrudes through the apertures, and forms pseudopodial stems from which the pseudopodia are produced. The pseudopodial stems fill the apertures entirely. Three regions in the cytoplasm can be differentiated. The two opposite regions near the apertures contain the contractile vacuoles, while the inner part of the endoplasm contains the nucleus, the food vacuoles and some cytoplasmic granules. The two contractile vacuole systems are working alternately; each contains 1-5 contractile vacuoles. The vesicular nucleus is central, eccentric or peripheral with one spherical nucleolus. There are up to 30 spherical, endogenous, bright granules in the cytoplasm.
Two types of pseudopodia can be distinguished. One is a rather thick, long, straight, tubular, unbranching pseudopodium, which tapers only at the distal region. The other type is a much thinner, parallel sided or tapering filopodium. The thick pseudopodia may be as long as 20-25 µm. They may bend slowly in the surrounding water, or they may break and become zigzag. One or two thick pseudopodia are produced per aperture. When two are produced, they usually branch immediately at the aperture, and they are directed oppositely and perpendicularly to the longitudinal axis of the cell. The thinner filopodia may reach lengths similar to the thick ones (up to 28 µm).
No gliding movement on the surfaces of the filopodia could be observed. The cell changes its position by changing the angles of filopodia. A slow movement is achieved, when the cell retracts back a thick pseudopodium, which is attached distally to the surface. When the two thick pseudopodia are oriented oppositely, the cell may glide back and forth by this track. The pseudopodia do not glide even in these situations.
The rigid and narrow aperture strictly limits the size of the ingestible food particles. The length of ingested bacteria exceed the diameter of the aperture, but their widths are certainly lower. Only bacteria (mostly bacilli) have been found in the food vacuoles. Food vacuoles may remain solitary, but they often fuse to large collective food vacuoles. Only one collective vacuole per cell was observed, it was situated next to one of the contractile vacuole systems.
(All information after Kiss et al, 2009)