Strange Butterfly

When out for our walk yesterday, we watched seagulls picking up mussels in their beaks, and then they took off and climbed to about 40 or 50 feet and dropped the shellfish on the rocks. Then the gulls would almost fall out of the sky, and proceed to peck away at the contents of the now broken shells. I have seen this before, but not recently. It was fun to watch. Then I got curious about how many mussels were actually around on the beach. I walked out on the beach to where the beach grasses grow - at this time of year there are just clumps of stumps of the grasses. And in amongst the grasses, what did I see but mussels growing. I pulled one out and it was clamped tight. So I got out my knife and cut it open - it was alive and growing. I had never noticed them on the beach before. I had seen shells, but didn't know where they grew. Anyhow, here is one, spread open. I thought it looked like a strange butterfly. No way I would take a chance at eating one, however.