Porifera
Porifera is a phylum of animals that consists of sea sponges. These sponges are often found on coral reefs, and have no circulatory, digestive, or nervous systems, instead relying on a system of pores that maintain a constant water flow through their bodies that provide oxygen and waste removal. Ironically, some species of sponges have skeletons that lie outside of their vital organs, and use these as protection, while attaching themselves to rocks, or other such things.