The axial cell is large and occupies about one third of the diameter of each branch, best seen in transverse section.

[2] Choreocolax polysiphoniae is a small parasitic alga which grows in a cushion-like manner to 1 mm in diameter on the branches of P.

[4] Widespread growing epiphytically on Ascophyllum nodosum wherever it is found and occasionally on other species of Fucus.

The tetraspores occur in spiral series[2] resulting from a simultaneous division into 4 equal spores.

[8] Common around the British Isles and on the shores of Europe from Iceland, Norway to Spain.