In this case a bi-valve. Shells are made up of calcium carbonate. They need a neutral water environment to grow and survive. But like so many problems we cause, we are damaging the oceans. The seas are slowly acidifying them. The oceans are now weakly acidic which is slowly affecting the growth of shells and corals. They cannot lay down the material they are made of as easily in the current environment. If things get worse we could lose many of these beautiful creatures (yes they are animal not plant life).
More to work on in the coming decade. If we don’t a large number of animals that eat shellfish may be affected. We really do have to think about it.