Brachiopods

The word brachiopods literally means Arm-legs, these animals belong to a separate tribe within the animal kingdom. Brachiopods are sea animals that filter food particles from the water. In the larval stage, they swim freely, but when they mature they anchor with their feet at the bottom (or other organism). Then they develop a hard shell around the soft body. Unlike the bivalves / Bivalves, these shells are not a mirror image of the other side. Barchiopods are already known from the Lower Cambrian and today there are still about 200 species. In the Paleozoic the brachiopods were much richer in species, but after the Permian trias extinction there are a handful left over. And the role has largely been taken over by the bivalves, which in fact fulfill the same role in the ecosystem.