| Group | Approximate number of living species described | Major subgroups, other names, and notes |
|---|---|---|
| Ctenophores | 250 | Comb jellies |
| Sponges | 8,500 | Demosponges, glass sponges, calcareous sponges |
| Placozoans | 2 | Additional species have been discovered but not yet formally named |
| Cnidarians | 12,500 | Anthozoans: Corals, sea anemones Hydrozoans: Hydras and hydroids Scyphozoans: Jellyfish Myxozoans: Parasitic mucous animals; sometimes placed in group distinct from cnidarians |
| Orthonectids | 45 | Microscopic wormlike parasites of marine invertebrates; relationships uncertain |
| Rhombozoans | 125 | Tiny (0. |
| PROTOSTOMES | ||
| Arrow worms | 180 | Glass worms |
| Lophotrochozoans | ||
| Bryozoans | 5,500 | Moss animals |
| Entoprocts | 170 | Sessile aquatic animals, 0. |
| Flatworms | 30,000 | Fre |
| Gastrotrichs | 800 | “Hairy backs” |
| Rotifers and relatives | 3,000 | Rotifers, spin |
| Ribbon worms | 1,200 | Proboscis worms |
| Phoronids | 10 | Sessile marine filter feeders |
| Brachiopods | 450 | Lampshells |
| Annelids | 19,000 | Polychaetes (generally marine; may not be monophyletic) Clitellates: earthworms, freshwater worms, leeches |
| Mollusks | 117,000 | Monoplacophorans Chitons Bivalves: Clams, oysters, mussels Gastropods: Snails, slugs, limpets Cephalopods: Squid, octopuses, nautiloids |
| Ecdysozoans | ||
| Kinorhynchs | 180 | Mud dragons |
| Loriciferans | 30 | Brush heads |
| Priapulids | 20 | Penis worms |
| Nematodes | 25,000 | Roundworms |
| Horsehair worms | 350 | Gordian worms |
| Onychophorans | 180 | Velvet worms |
| Tardigrades | 1,200 | Water bears |
| Arthropods | ||
| Chelicerates | 114,000 | Horseshoe crabs, pycnogonids, and arachnids (scorpions, harvestmen, spiders, mites, ticks) |
| Myriapods | 12,000 | Millipedes, centipedes |
| Crustaceans | 67,000 | Crabs, shrimps, lobsters and crayfish, barnacles, copepods |
| Hexapods | 1,020,000 | Insects and their wingless relatives |
| DEUTEROSTOMES | ||
| Xenoturbellids | 5 | Secondarily simple marine worms; relationships uncertain |
| Acoels | 400 | Very small (mostly <2 mm) flattened marine worms; relationships uncertain |
| Echinoderms | 7,500 | Crinoids (sea lilies and feather stars), brittle stars, sea stars, sea daisies, sea urchins, sea cucumbers |
| Hemichordates | 120 | Acorn worms and pterobranchs |
| Tunicates | 2,800 | Sea squirts (ascidians), salps, and larvaceans |
| Lancelets | 35 | Cephalochordates |
| Vertebrates | 65,000 | Hagfish, lampreys, cartilaginous fish, ra |