So far I have only found 2 specimens of Synoikomonas phaneros. Both originate from the Simmelried and had settled on the floating coverslip.

This interesting flagellate stands out due to its blueish-green color, which is caused by symbiotic cyanobacteria known as cyanelles. The flagellate is otherwise colorless. In Synoikomonas phaneros the cyanelles are arranged parietally directly beneath the pellicle. They were described very precisely by Skuja (1964). They are spherical and resemble cells of the genus Synechocystis. They are somewhat lighter in their central area. In DIC, the center of the cyanelles is contrasted as an area of increased optical density (s. fig. 2).

Synoikomonas phaneros swims quite fast, whereby the propelling (pulling) leading flagellum is considerably shorter than the long trailing flagellum (s. fig. 1 b). The contractile vacuole is clearly subapical, just like the pharynx (s. figs. 1 b and 1 f). In his population, Skuja localized the nucleus near the middle of the body. In my specimens it was clearly located in the anterior half (s. fig. 1 f). In addition to the cyanelles, the cytoplasm is filled with small, somewhat irregularly shaped starch granules (s. fig. 2).

Synoikomonas phaneros can easily be confused with flagellated swarmers of Gloeochaete wittrockiana. This alga also has symbiotic cyanelles and it can form mobile swarmers with a leading flagellum and a trailing flagellum. However, the swarmer of Gloeochaete wittrockiana are only 18–25 µm long (Skuja, 1956) and the cyanelles are comma-shaped and not spherical as in Synoikomonas phaneros.