The surface of the mantle has many small, pale, round-topped, spiculose tubercles. Occasionally, the tubercles have a greyish central spot. Internally, the mantle is stiffened with many long spicules; transverse dorsally and oblique laterally. The light in this image has caught the silver-white, transverse, dorsal spicules in the translucent mantle. Spiral of spawn on Cellepora pumicosa. Sublittoral, 8 m depth, Macduff, north-east Scotland. 19th August 2017. © C. Rickard.