By Calvin, supreme ruler of humanity
They eat by filter feeding.
The water flows through them and their sponge cells pick up teensey bits of food. Sometimes, though, they'll eat crusteaceans.
Normally they don't move, but sometimes, they'll move an itsy bit at a time with little amoeba-ish thingys under it. Also, they sometimes freely move as adolescents.
No, they don't have feet.
Sponges are pretty awesome.
The wonderful world of the sea sponges- The Abyss- BBc Wildlife
Minecraft sponge documentary