The eight major phyla of invertebrates are Porifera, Cnidaria, Platyhelminthes, Annelida, Nematoda, Arthropoda, Echinodermata and Mollusca. There are also minor phyla. Most animals are invertebrates, and most of those are arthropods.
Sponges are members of the phylum Porifera. They look like plants and were once thought to be plants. They live attached to substrates on the ocean and filter out their food from the currents of water.
Cnidaria are also simple, aquatic animals. These include sea anemones, jellyfish, corals and hydroids. Unlike sponges, they have bodies that are radially symmetric, which means one side resembles the other if the animal is cut in half.
Platyhelminthes are flatworms. Some of these worms, such as tapeworms, are parasitic. Annelida are also worms and include the earthworm and the leech.
Nematoda are roundworms, or nematodes. Like Platyhelminthes, they can be parasitic or free living.
Members of Arthropoda have a protective exoskeleton and bodies that are divided into segments. They include crustaceans such as lobsters and crabs, insects, spiders, centipedes, millipedes and scorpions.
Members of Echinodermata include starfish, sea stars, sea urchins and sea cucumbers.
Animals in the phylum Mollusca have the greatest variation in body shape. They include octopuses, squid, oysters, clams, snails and slugs.