Biologic evolution

It is a mussel that keeps it in the water tank of Waca. The mussel of a large individual has died. It is two. mussels of a small individual the remainderIt doesn't understand in detail because there is no picture book in the internal organs part of the mussel. I do not think that there is the gills part of the shellfish.The shell seems to play the role of the gills by the mussel. It is imagined that it is because there are no one gills to live in the region where the place and the water current with the currents are extreme.The mussel opens and shuts the shell. Oxygen might be taken into the shell by being able to do one space so that the water current may flow to the shell when opening. (Please refer to the article on opening completely for the space in the shell. )In the photograph, the mussel put Tait on the stone that the air pump previously put up. It was thought that the purpose was to take the flow of air to the shell.