Jellyfish belong to the phylum Cnidaria. Cnidarians are a group of invertebrates that have radial symmetry, a single opening to the digestive system, and stinging tentacles. They include jellyfish, corals, sea anemones, and hydroids.
Porifera are a group of invertebrates that have a porous body and no true tissues. They include sponges.
Nematoda are a group of invertebrates that have a long, cylindrical body and a pseudocoelom. They include roundworms.
Mollusca are a group of invertebrates that have a soft body and a hard shell. They include snails, clams, and octopuses.
Jellyfish are more closely related to corals and sea anemones than they are to sponges, roundworms, or mollusks. This is because they all share the same basic body plan, which includes radial symmetry, a single opening to the digestive system, and stinging tentacles.