Before and after outer epidermis sloughed. Left: before slough.
Centre: ten days later, post-slough. Right: sloughed outer epidermis.
The dorsal surface often has marks of white, orange, yellow, black, and/or red that may cover almost all the ground colour.
Sometimes an outer layer of epidermis is sloughed (Bate in Forbes & Hanley 1853), resulting in the loss of the majority of the sculpture and colour,as in this case, or ,sometimes, revealing fresh, bright colours (see fig 11).
This live sloughed specimen is translucent revealing some internal features.The shape of the shell and its protruding spire (s) can be detected by the viscera covered by it.

Visible visceral features (numbered to accord with features in fig.17 ) include:
3: brown, bipectinate osphradium that tests the water quality of the inhalent current and, possibly, filters out large debris before the current reaches the ctenidium.
4: large, pale orange, unipectinate ctenidium (gill) with very long filaments.
8: convoluted hypobranchial gland that shows as a series of irregular white bands on the mantle. It secretes mucus for trapping and cementing particulate matter from the inhalent current before it is expelled.
9: kidney.
10e: bright purple-pink posterior lobe of capsule gland (only on females).

Length 21 mm. March 2013. Menai Strait, Wales.