Test washed up on the beach.
No interactions present.
I agree that this is probably is E.cordatum. This species is common on muddy sand off the Northumbrian coast and in the picture the indentation at the anterior of the test is quite deep.
Its always worth bearing in mind there are two other species of the genus that are difficult to seperate on the basis of a naked test; E.flavescens (generally yellower in colour when alive and on coarser sediments) and E.pennatifidum that has long spines only anteriorly
Lat/Lng: 55.6126, -1.7106
OS grid ref: NU183354