Marine Sea Worms consist of three main phyla - Platyhelminthes (Flatworms) - Nematoda (Roundworms) - Annelida (Segmented worms) Interesting facts: - Worms in general are found on land and in the ocean - All worms of the phylum nematoda are parasitic - Platyhelminthes have no coelom, nematoda have a pseudocoelom, and annelida have a true coelom. Field Guide Sea Worm: Planarian (Phylum platyhelminthes, Planiara simplex)