Yellow/orange form may be restricted to the Lille Belt, Denmark. 1: opaque central column of spicules splayed out to protrude from some tubercles. 2: tubercle filling posterior gap in orange gill ring. 3: small tubercle within gill ring, number varies 0 to 3. 4: opaque pigment at base of gills is usually white, but yellow on this strongly coloured form. 5: bright orange gills (and rhinophores) on this form. On white forms just slightly yellowed. Lille Belt, Denmark, February 2018, © B. Picton.