In April 2026 I found Phacus alatus in large numbers between floating plant material in the Simmelried. Otherwise I find this species only very rarely.

Phacus alatus has a compact shape with a sharply curved, short caudal spine. The cells often have an asymmetrical form because the two halves of the cell can be slightly different in size. Striking are two large paramylon grains, which lie laterally (s. fig. 1 a). They are so large that they deform the cell and noticeably thicken it. There are additional, much smaller paramylon grains, all of which are round. The eyespot is conspicuously large. I was not able to document the flagellum, because the specimens reacted very sensitively to the coverslip being placed on them and immediately shed the flagellum.

The specimens of my population were around 50 µm long. It is difficult to say what the maximum dimensions of this species are, since Phacus alatus has meanwhile been synonymized with several other (larger) species such as Phacus platyaulax or Phacus macrostigma. In the cytoplasm of the specimens of my population there were quite a lot of haematochrome granules, which were not mentioned by earlier authors (s. fig. 2 d).