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Leptomyxa fragilis (Penard, 1904) Siemensma, 1987

Diagnose: Large amoeba, polypodial form usually covered with detritus; numerous small nuclei, each with 1-3 irregular shaped nucleoli; cytoplasm clear, sometimes with some small mineral grains and diatom frustules; subpseudopodia often broadly lobed with a deep incision between the lobes; several contractile vacuoles, which can grow large and sometimes melt together; no crystals; hyaloplasm at the anterior end, with eruptive bulges; hyaloplasm may run back along the sides, just as in Rhizamoeba-species.

Dimensions: My measurements 250-480 µm, nuclei 6.2-8.4 µm (Penard 5-7 µm); Penard (1890) gives as mean 180-300µm, but his stained mounts in the collection of the Natural History Museum in London contain three specimens with the following dimensions: 398, 403 and 456 µm.

Ecology: Fresh water. I found this species in sediment of a small forest stream near Epe (1980), the Netherlands.

Remarks: It is possible that this species is identical with L. reticulata. The photomicrographs 11 and 13 of Pussard (1976) resemble strikingly the specimens which I observed. However, I have never seen the flat plasmodium. This form is probably only  employed on agar. Both Pussard (1976) and Goody (1914) state that the nuclei of L. reticulata usually have one nucleolus. Penard has seen one, two and three nucleoli.
The number of nuclei are numerous. Penard speaks of several hundreds. I could see this in his stained slides in London. In one mount I could count more than two hundred nuclei. I have tried to count the number of nuclei in my specimens. I stained one amoeba with borax-carmine and counted more than 400 nuclei.
Remarkable are the large vacuoles, the largest reaching a diameter of 41 µm. In the London collection these large vacuoles were also visible.

Leptomyxa fragilis
Leptomyxa fragilis, after Siemensma, 1987
Leptomyxa fragilis
Leptomyxa fragilis, after Siemensma, 1987
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