The document discusses several invertebrate animal phyla, including sponges, cnidarians, flatworms, roundworms, and segmented worms. Sponges are the simplest animals and have a skeleton made of spicules to support their body. Cnidarians like hydra, jellyfish, and corals have stinging cells called nematocysts that they use for defense and capturing prey. Flatworms are flat ribbon-like organisms including parasitic tapeworms and free-living planaria. Roundworms have long cylindrical bodies and include parasites like the trichina worm as well as soil decomposers. Segmented worms have a segmented body and include earthworms, leeches, and