海绵是世界上结构最简单的多细胞动物。说它简单,是因为它既没有头,也没有尾,没有躯干和四肢,更没有神经和器官。海绵虽然属于动物,但是它不能自己行走,只能附着在海底的礁石上,从流过身边的海水中获取食物。 Sponge is the simplest multicellular animal in the world. It is simple because it has neither head nor tail, no trunk and limbs, and no nerves and organs. Although the sponge is an animal, it cannot walk on its own, but it can only be attached to reefs on the sea floor to obtain food from the sea water that flows through it.