PLATYHELMINTHES Eumetazoa: Bilateria: Phylum Platyhelminthes (flatworms) marine, freshwater, terrestrial

PLATYHELMINTHES either Protostomia or Lophotrochozoa triploblastic: 3 germ layers ectoderm: epidermis, nervous tissue mesoderm: true muscle tissue endoderm: gastrodermis lining gastrovascular cavity acoelomate

PLATYHELMINTHES lack some organ systems (circulatory, respiratory) diffusion: reason why small and flat have others (muscular, nervous, digestive, excretory, reproductive) nervous system (Fig. 49.2): eye spots, rudimentary brain, nerve cords cephalization (head); Fig , Fig. S4-2

PLATYHELMINTHES hermaphroditic: male and female reprod. systems in same individual adaptive advantage: every individual potential mate digestive system: mouth, pharynx, gastrovascular cavity one way gut; no anus invagination: increases surface area

PLATYHELMINTHES excretory system: protonephridia (Fig ); proto = first, nephrus = kidney branching network of tubules flame-bulb cell with cilia draws mostly water, some waste into tubules exit via nephridiopores

PLATYHELMINTHES free-living (non-parasitic) ancestral life history many parasitic in vertebrate gut suckers/hooks; Fig. S4-3 reduce/lose some ancestral characters tapeworms: no mouth/gastrovascular cavity/excretory structures; diffusion mostly reproductive organs Fig

MALFORMED FROGS mystery of the malformed frogs August 1995: school kids in MN, field trip to a pond; amphibian malformation

MALFORMED FROGS most states, range of deformities hypothesis: endocrine disrupting chemicals disrupt development by disrupting hormones

MALFORMED FROGS alternative: trematode hypothesis trematodes (= flukes) Ribeiroia life cycle: encysts in limb buds

MALFORMED FROGS can cause deformities, but why now? human-caused ecosystem disruption nutrient runoff: organic pollution (fertilizer, manure, sewage) increased snail population (a key host) modified hypothesis: nutrient-trematode

NEMATODA Eumetazoa: Bilateria: Phylum Nematoda (roundworms)

NEMATODA Protostomia or Ecdysozoa pseudocoelom complete digestive tract (2 openings) hangs free in pseudocoelom; Fig. S5-1 cylindrical, unsegmented body cuticle: tough, thick outermost layer around epidermis; ecdysis

NEMATODA hydrostatic skeleton: fluid in pseudocoelom; high pressure nervous system: anterior nerve ring, dorsal/ventral nerve cords no circulatory/respiratory systems; diffusion muscular system: longitudinal muscle locomotion: contraction; thrashing

NEMATODA only sexual reproduction (Fig. S5-2) some hermaphroditic, others dioecious dioecious: separate male, female reprod. system fills most of organism

NEMATODA free-living (soil); parasitic uniform structurally, diverse ecologically species differ in specific habitat probably over one million species: speciose 1 sq m of marine mud: 4.5 million individuals!; very successful much to be learned

NEMATODA Caenorhabditis elegans (C. elegans) model organism free-living soil nematode; easy to raise transparent; life cycle: 3½ days every cell mapped, fate known; Fig

C. elegans entire genetic sequence known huge medical applications humans, nematodes both bilaterians evolutionary medicine: studying other organisms for insight into humans

ANNELIDA Eumetazoa: Bilateria: Phylum Annelida (segmented worms) Protostomia or Lophotrochozoa coelomate segmentation: repeated muscular, nervous, excretory elements divided by septae annelida = little rings Fig

ANNELIDA hydrostatic skeleton: fluid in coelom circulatory system: closed; Fig. S6-3 heart: muscular blood vessels dorsal, ventral blood vessel; Fig. S6-1 capillaries: small branches of blood vessels

ANNELIDA excretory system: metanephridia (Fig ) fluid enters nephrostome, passes through coiled tubule useful nutrients return to circ. system, wastes excreted via nephridiopore

ANNELIDA nervous system: ventral nerve cord with ganglia (swellings); brain muscular system: longitudinal and circular muscles locomotion: muscular contraction works against hydrostatic skeleton of coelom setae (bristles) digestive system: subdivided and more specialized hermaphroditic or dioecious

ANNELIDA leeches specialized as predators or blood feeders don’t confuse with trematode no obvious head; no septae or setae suckers for temporary attachment large digestive system for blood secrete hirudin: anticoagulant other secretions; osteoarthritis