[Image:commensal hydroid7.jpg|thumb|200px|left|hydroid overgrowth on the shell]The scaly dogwhelk is a small brownwhelk with many fine knobbly spiralridges on its shell. It grows up to 5 cm in total length. The ridges of the snail's shell are not often visible because the whelk is usually overgrown by the high-spined commensal hydroid, Hydtractinia altispina, which looksprickly and is orange.