Polychaos dubium (Schaeffer, 1917)
In the early spring of 2012 and 2015 I found large number of specimens of Polychaos dubium in floating debris at several locations around the Naardermeer. These specimens were completely filled with food particles and large paired bodies, thus resembling a Pelomyxa species. Because they were filled with food particles, they probably didn't show a more slender and palmate shape as is characteristic for Polychaos. At first sight these specimens are hard to distinguish from Pelomyxa, being broad and without pseudopodia and fully filled with food and debris. One specimen contained a large quartz particle. Only when they start to move, you can see that the monopodial form lacks the fountain streaming of Pelomyxa, though specimens which doesn't adhere to the substrate, also show this fountain streaming.