Codium tomentosum is a green macroalgae with a dark green cylindrical thallus that branches dichotomously. In this specimen, the thallus is approximately 16 cm long, although the species can reach up to 40 cm. 

The branches have a spongy texture and a surface resembling Velcro, due to the presence of numerous colourless hairs covering the thallus, which are only visible when submerged.

It is anchored to the substrate by numerous fine rhizoids which, due to their density and the accumulation of sand at their base, may give the impression of a holdfast disc, from which the main branches emerge.