1. Invertebrates 2 Ctenophora, Platyhelminthes, Nematoda

2. Lecture outline 1.Phylum Ctenophora (briefly) 2.Phylum Platyhelminthes 3.Phylum Nematoda

3. Phylogenetic overview (cont.)

4. Phylum Ctenophora: The comb jellies  Along with Cnidarians, they are radially symmetrical

5. Phylum Platyhelminthes: The flatworms

6. Evolutionary position: Development of a third germ layer and bilateral symmetry  Cnidarians, Ctenophores All others  Radial symmetry, diploblastic Bilateral symmetry, triploblastic  (Porifera)

7. Still no body cavity!  Platyhelminthes All others have body cavities  Porifera Cnidaria  Ctenophora

8. Basic Platyhelminthes features  Eversible pharynx  Gastrovascular cavity  Structure  Functions  Water and ion balance  Nervous system  Unidirectional AP  brain  distinct nerve cords sensory organs  Movement

9. Reproduction  Hermaphrodites  Internal fertilization  penis, sometimes with stylet  hypodermic impregnation  stab prey  R-rated flick…

10.  The blood fluke Schistosoma infects 200 million people, leading to body pains, anemia, and dysentery. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 33.11

11.  Tapeworms (class Cestoidea) are also parasitic.  The adults live mostly in vertebrates, including humans.  Anterior suckers and hooks anchor the worm in the digestive tract of the host.  A long series of proglottids, sacs of sex organs lie posterior to the scolex.  Tapeworms absorb food particles from their hosts. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 33.12

12. Phylum Nematoda: The roundworms

13. Evolutionary features: Body cavity!  Platyhelminthes Nematoda and all others!  Porifera Cnidaria  Ctenophora

14. Nematode body cavity: pseudocoelom  Mesoderm on inside of body wall, but not surrounding gut

15. Body plan  Feeding/digestive system:  Relatively simple (not highly branched) gut, but it is complete, with anus!  Gas exchange  Body surface  Coelomic cavity  No circulatory system  Excretory system/osmotic regulation  Exists, not well-understood  Locomotion:  Have only longitudinal muscles  Demo: The nematode swim!

16. Body plan (cont.)  Nervous system  Four nerve cords: 1 dorsal, 1 ventral, and 2 lateral  ganglia along ventral cord (will see this in arthropods/annelids)  Sensory structures

17. Reproduction, etc…  Reproduction  Sexes usually separate, but some hermaphrodites  Internal fertilization  Many parasitic forms  Trichina worms  Heartworms  River blindness  Elephantiasis  Also parasitic in plants