What you have there is a small clutch of Cockles
, and if you want to try them they can be prepared in a variety of ways, even raw.
If cooking in the shell, soak them in clean water for an hour or so, so they have a chance to flush out the sand and dirt.
If raw just wash thoroughly with clean water.
If you have an aquarium they can be kept alive, but they can become a food source depending on the other species of aquatic life in your tank.
It is possible they can produce pearls, but they are not as prolific as Oysters.
Be careful where, and how you collect them as there may be regulations on harvesting and you could be setting yourself up for a modest to large fine if caught doing it.
If your serious, check with fish and game authorities, watermen, or friends on local customs and practices.
This article from the London Times says it is okay, but it is two years old. I would still check:
Catch your own shellfish supper
Grab your bucket and net and head for the coast — it’s fresh, fun and free
Source: Catch your own shellfish supper - Times Online