Juvenile shell transitioning to adult form.

Final stage juvenile shell is often larger than some adults. This appears to be because the mantle changes in parts to resorb, instead of deposit, calcium carbonate during change to adult. This was disputed by Forbes & Hanley (1853), but close examination of specimens undergoing the change show grooves cut below (1) the level of the yet unaffected juvenile areas (2) of the shell, leaving ribs of juvenile shell between the grooves.

Mantle extends from slit aperture (3) on both sides to cover exterior of shell. Area close to aperture is covered by mantle most frequently, and develops grooves earlier and more deeply than summit (4) of shell, but remains white. Further up the shell, a very thin layer of pink shell (5) is deposited in the cut grooves. The spire (6) is almost enveloped by the final whorl.

Length 8.3 mm. South-west Portugal. December 2019. Leg. A. Rodrigues.