Platyhelminthes Nematoda Annelida

Phylum Platyhelminthes- Flatworms  Bilateral symmetry  Acoelomate – no developed middle layer  solid body without a space in the center  Gastrovascular cavity with one opening  Some respire (breathe) directly through skin

Platyhelminthes  More advanced nervous system than Porifera/Cnidaria  Shows Cephalization- development of the head end  Development of a BRAIN

Platyhelminthes

Platyhelminthes tapeworm

Platyhelminthes flukes

Nematoda (Roundworms)  NON-segmented!!  Bilateral Symmetry  Pseudocoelomate – have a “false” middle layer  a fluid filled body cavity  Complete digestive tract (two openings)  Many are parasitic  Abundant (as many as roundworms in one rotten apple!)  C. elegans first multicellular animal to have its complete DNA sequenced  Also have Cephalization (Brain)

Nematoda

Life cycle of Nematode animal parasite

Annelida (Segmented worms)  Coelomate – have a true middle layer (most advanced)  Segmented  Bilateral Symetry  Complete digestive tract  Closed circulatory system (earthworms have 5 hearts)  Paired setae (bristles) for movement  Cephalization

Earthworms - Oligochaetes  True body cavities and segmentation are important evolutionary adaptations!!

Marine worms - Polychaetes  Many setae brushlike structures  Some have tentacles and eyes

Marine Worms - Polychaetes

Leeches - Hirudinea  No or very few setae  Mostly parasitic one-fourth carnivorous