Species:

Note: This is a rather rare southern species at the Norwegian coast and is distributed north to the Trondheimsfjord. It can be confused with Ceramium tenuicorne, since both are thin and have conspicious ecorticate internodes of main axes, and tightly inrolled apices. It separates from this species by having wide angles between branches (> 60 degrees, while C. tenuicorne has 30-45 degrees), and swollen, protruding cortical bands, which are often wider in the upper than in the lower part. Contrary to C. tenuicorne it may also have gland cells. C. diaphanum usually developes only one tetrasporangia in each cortical band, while C. tenuicorne developes a ring of tetrasporangia in each band and additionally often carries parasporangia.