The picture shows the structural schematic diagram of the mussel. Please answer the following questions according to the picture. (1) There are two calcareous shells with similar size outside the mussel, so it is called _ _ _ (1) The mussel belongs to mollusk, and it has a shell outside, which plays a protective role. The two soft and thin membranes that cling to the mussel shell and wrap the visceral mass are called the mantle. The mantle is composed of inner and outer epidermis, connective tissue in the middle and a few muscle fibers. The side close to the viscera is the inner epidermis, and the side attached to the shell is the outer epidermis, which has the function of secreting nacre to form pearls.

(2) mussels belong to mollusks and breathe through gills;

(3) The mussel belongs to mollusk and moves with its axe feet;

Therefore, the answer is: (1) double shell; Mantle; Mantle;

(2) gills;

(3) Axe foot