| The short answer to the latter question is that sponges are animals, although it took the development of the microscope to finally resolve the issue. Typically, plants derive their nourishment from the soil elements, water and air, while animals feed on living things, or the organic matter derived from them. Sponges feed by filtering living and dead organic matter from the water.
A sponge is basically a bunch of cells loosely connected together. Unlike most other animals, sponge cells do not aggregate into tissues, or groups of specialized cells which can then form such things as organs. This means sponges do not have such luxuries as nerves or muscles, blood or even a mouth or a digestive cavity.
Instead, a sponge is a mass of 'flesh' perforated by hundreds or thousands of canals and chambers, linked to the outside by pores. These canals are lined with specialized cells each of which has a hair or whip-like end. The beating of these hairs flushes water through the sponge, bringing with it microscopic food particles and oxygen for respiration.
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