CH34: Phylum Platyhelminthes Flatworms

Characteristics of Platyhelminthes Thin, flat body (acoelomates) Bilateral symmetry 3 tissue layers Endoderm Ectoderm Mesoderm organs and muscles, not present in Cnidarians or Porifera Cephalization

Free-living flatworms are carnivores Do not have respiratory or circulatory system Diffusion of gasses Branched cavity with extensions that run into all major tissues Gastrovascular cavity Flatworms reproduce sexually or asexually. fragmentation

Characteristics of Flatworms

Groups of Flatworms Three major groups of modern flatworms include; Class Turbellaria, most free-living and some marine,ex Dugesia Class Cestoda, parasitic tapeworms, ex. Taenia Class Trematoda, endoparasitic flukes, ex. Fasciola Class Monogenea, mostly ectoparasites on aquatic animals Species range in size from less than 1mm to many meters in length.

Class Turbellaria Planarians and marine flatworms

Class Trematoda Flukes Involve several host Schistosomiasis blood disease from contact with contaminated water

Class Monogenea Fluke Ectoparasite

Class Cestoda Tapeworms Largest group of endoparasites Tegument on tissue Hooks to attach to host (Scolex) Proglottids to reproduce