Juvenile.

1: anterior inhalent siphon.

2: fine grey/black particles coalesce to form spots grouped into dark discs.

3: double series of lateral folds (resembles bipectinate ctenidium) of yellow comb-like osphradium (for testing water quality), indistinctly visible in mantle cavity through juvenile shell.

4: long yellow ctenidium in mantle cavity visible through juvenile shell, unipectinate but too indistinct for lamellae to be distinguished.

Shell length 9.3 mm. Anglesey, Wales, September 2015. Leg. J. Light.