Spawn of both forms is a thin line in a smooth spiral when on flat substrate.
The whole tip of each ceras is covered by a substantial cap of opaque white, except for a small, translucent apex which, when viewed end on, can reveal the rust-brown digestive gland as the ‘brown spot’ recorded by Sars (1829).
Southern Norway, April 2006. © CC BY-NC-ND, A. Hansen. www.flickr.com/photos/xoto/