Coquina on Sanibel Shoreline

At the beach on Sanibel and I noticed these tiny shells all over the shoreline but didn't really pay attention. Then later started noticing they would disappear everytime a wave came and then they'd re-appear. So...I switched on the video and went in for a closer look. It really grossed us out! But I checked in a shell book later than night and found they are Coquina a small live clam that lives in abundance along Atlantic shores. Never saw them before or since...but they were pretty cool to watch...