One class in this phylum is distinguished by its posterior-end opisthaptor, a second class has an anterior-end scolex, and a third class has sub-epidermal rhabdites.  They contain filling tissue known as parenchyma, and some species have photoreceptors known as ocelli.  Some species of this phylum engage in penis fencing, while cross-fertilization 
One class in this phylum is distinguished by its posterior-end opisthaptor, a second class has an anterior-end scolex, and a third class has sub-epidermal rhabdites.  They contain filling tissue known as parenchyma, and some species have photoreceptors known as ocelli.  Some species of this phylum engage in penis fencing, while cross-fertilization and transverse fission are common in the cestodes and the free-living turbellaria, respectively.  These triploblastic acoelomates are unsegmented and bilaterally symmetric.  Flukes and tapeworms can be found in, FTP, this phylum of flatworms.
One class in this phylum is distinguished by its posterior-end opisthaptor, a second class has an anterior-end scolex, and a third class has sub-epidermal rhabdites.  
Platyhelminthes (prompt on flatworms)