Phylum: Platyhelminthes (pla-tee-hel-min'-theez): flatworms. These worms have a head and bilateral symmetry. They have true organs but only one opening into the gut. They have no respiratory or circulatory systems and no coelom. Many forms are parasites including flukes and tapeworms while others are predatory. Click for two flatworms. One beautiful; the other ugly???