About the size of a golf ball.
No interactions present.
We used to call these sand dollars, these may be the skeletons.
Usually 'sand dollar' is applied to other echinoderms in the Clypeasteroida, not especially closely related to urchins. They are much flatter. We have one in the group in UK , Echinocyamus pusillus, but that is only 1cm long.
PS - I meant to add that the heart urchins are sometimes known as 'sea potatoes' for fairly obvious reasons.
recording wildlife with The Recorder's Year on www.hbrg.org.uk/TRY.html.
Many thanks everyone.
Lat/Lng: 40.765, 24.591
Found on the beach following a stormy winter.