Originally, this colony-forming flagellate was called Spongomonas intestinum. This name was given by Stein in 1878. However, it turned out that Cienkowski had described the same organism 8 years earlier as Phalansterium intestinum.

I find Phalansterium intestinum very frequently, especially among floating plant masses. Phalansterium intestinum is particularly easy to isolate in old samples, as the colonies often settle on the vessel walls, where they can be recognized as brown flakes.

The colonies are vermiform and can be several centimeters long (s. fig. 1). They are usually orange-brown in color. The colonies consist of a gelatinous matrix in which many spherical granules are embedded (s. fig. 4). Close to the surface are the spherical cells are located, which build up the colonies. They are embedded in the matrix up to the anterior end. From there, the two flagella of equal length are extended to swirl food towards them. The inner structure of the cells is difficult to recognize due to the opaque matrix. In addition, the cells react sensitively to coverslip pressure and leave the colonies. The released cells can then be examined more closely. According to my observations, the contractile vacuole is not located at the posterior end, but at the level of the cell equator (s. fig. 6).