Final answer:
Sponges belong to the phylum Porifera, characterized by their porous bodies and filter feeding behavior. They are primitive multicellular organisms without true tissues. The classification as Porifera reflects their unique morphology and aquatic lifestyle.
Step-by-step explanation:
Sponges are simple multicellular organisms that are classified within the phylum Porifera, meaning "pore-bearer". This name reflects their distinctive feature: a body full of pores that allow water to flow through. These aquatic invertebrates exhibit a primitive level of organization lacking true tissues and body symmetry but have specialized cells that perform various functions. Sponges have an endoskeleton made up of collagen, and some species also have silica-rich spicules.
Due to their sessile nature, sponges are filter feeders. They rely on the circulation of water through their porous bodies to filter out food particles, absorb oxygen, and excrete wastes. These essential functions are indicative of their adaptation and success as organisms that have survived unchanged for hundreds of millions of years.