Porifera (sponges)

Cnidaria (jellyfish, sea anemones, sea fans, soft corals, hard corals)

Ctenophora (comb-jellies)

Bryozoa

Crustacea (crabs, lobsters, barnacles, isopods, amphipods) 

Annelida (segmented worms) 

Pogonophora

Marine worms living in tubes. Some giant species, 1.5 m long have been found around warm water vents in the Pacific Ocean.

Vestimentifera

Echiura (spoon worms and innkeepers)

Once placed with the phylum Annelida.

Mollusca (snails, mussels, squid, etc.)

Sipuncula (peanut worms)

Nemertea (ribbon worms)

Marine worms that in some species can reach 30 m in length! Synonyms: Nemertini or Nemertina.

Platyhelminthes (flatworms, tapeworms) 

Hemichordata

Marine organisms such as acorn worms.

Brachiopoda (lamp shells)

Look superficially like clams in that they have a similar shaped shell but they are not molluscs.

Ectoprocta (bryozoans or moss animals)

Found on rocky shores.

Phoronida

Chaetognatha (arrowworms)

About 70 species known.

Echinodermata (starfish, sea urchins, sea cucumbers, etc.)