I learn a lot by doing my nature notes and knowing virtually nothing about sea shells and the creatures that live in them this particular area has been an eye opener! This particular shell is one often found on Studland beach but I had no idea what it is (was?).
As far as I can establish, based in the shelf that seems to cover the open section, this is the slipper limpet (Crepidula fornicata). It is an invasive species that came to our shores in the nineteenth century and has become abundant around the south, west and east coast of England. It is prolific and can form large reefs of shells, usually beyond the tidal zone and so are constantly under water. They grow in towers with the females at the bottom of the tower and the males at the top with those in between progressively becoming less female and more male as they go up the tower. It is a complex and strange process which, even having read about it, I cannot understand nor explain so if you are interest you will need to look it up in a book or on the internet!
It is an edible shell fish and is described as being different in taste to most other shellfish. It is considered 'versatile' and can be used as a meal on its own, as an appetiser when used in small quantities or it can be combined with other foods to make a mixed meal.