Ceramium diaphanum is a species of marine red algae (or Rhodophyta).

This small filamentous alga grows attached, or unattached, in masses reaching 20 cm across.

The branches grow pseudochotomously the tips are strongly coiled in.

[3] Growing as attached or unattached clumps on other algae and Zostera at low littoral to 3 m deep.

[3] Widely distributed in Ireland, England and Scotland.