Sponges—from the phylum Porifera (Latin for porus, meaning “pore,” and fera, meaning “bearing”) are thought to represent the most primitive animals. These organisms are collections of specialized cells without true tissues or organs, and their bodies are not symmetrical. They have a specialized way of gathering nutrients from waters and are known as filter feeders. (For more about sponges, see the chapter “Aquatic and Land Animal Diversity.”)