Ceramium echionotum is a small marine alga in the division Rhodophyta.

[1] It consists of large cells forming erect cylindrical filaments which are basically monosiphonous.

The thalli grow in a rather tangled manner, matted at the base by rhizoids.

In the British Isles, only Ceramium echionotum has spines formed of single cells which grow on the cortical bands.

[1] The species is dioecious producing spermatangia, carposporangia and tetraspores.