Flat Round and Segmented Worms Tripoblastic Acoelomate Pseudocoelomate

Flat, Round and Segmented Worms Tripoblastic, Acoelomate, Pseudocoelomate and Coelomates

Phylum Platyhelminthes Acoelomates with gastrovascular cavities Usually flattened dorsoventrally Unsegmented Bilateral Symmetry Incomplete gut usually present Cephalization-anterior cerebral ganglion with longitudinal nerve cords, some transverse nerves • No circulatory system • • •

Class Turbellaria • Free living flatworms named for the turbulence their cilia create in the water • First Bilaterally symetrical animals, characteristic of active lifestyle • Bottom dwellers in marine and freshwater , few terrestrial species in tropics • Predators and scavengers, some herbivores

Turbellaria Locomotion • Ventral surface contains gland cells, • Rhabdites secrete mucus to glide on, protect body • Adhesive glands stick to surfaces, Releaser glands dissolve attachment • Ectoderm layer with cilia or microvilli • Circular, Longitudinal and oblique muscles for locomotion and to maintain body shape • Movement by Cilia and muscular undulations

Turbellaria Digestion • Blind Digestive cavity, Varies from simple chamber to a highly branched chamber with digestive tubes, compensates for lack of circulatory system • Tubular Pharnyx for ingestion, varies from simple ciliated tube to a folded muscular organ • Food digestion starts extracellular, Phagocytosis engulfs small particles, intracellular digestion

Turbellaria Elimination • Gas exchange CO 2 and O 2 thru body wall, no respiratory organs • Protonephridia form networks of fine tubules thru body, collect excess water pumped by cilia expelled by nephridiapore • Allowed osmoregulation in fresh water

Turbellaria Nervous System • Cerebral Ganglia ( sometimes Paired ) at anterior end, Brain • Several pairs of long nerve cords run length of body • Lateral branches connect nerve cords, ladderlike appearance • Organized into Sensory ( to brain ), motor (away from brain ) and association (connecting), one way nerves

Turbellaria Reproduction • Asexually by transverse Fission, constriction behind pharnyx, two animals result regenerate missing parts • Monoecious, each animal contains ovaries and testes • Cross fertilization by exchange of sperm • Eggs laid in mass, some produce hard cocoon, summer thin cocoon, winter thick cocoon

Class Trematoda • Parasitic Flatworms, Flukes, wide flat shape • Almost all parasites of vertebrates • Feed on host cells, mouth and muscular pumping pharnyx • Digestive tract two blind pouches, Branched • Outer Layer of body called Tegument • Covered by proteins help protect fluke form host enzymes and immune system

Trematoda • Parasites in blood streams, digestive tracts ducts of digestive organs, and visceral organs. • Chinese Liver Fluke, in Asia 30 million people infected, snail- fish- Human, can infect sheep and humans who eat watercress • Schistosomes- Blood Flukes, infect 200 million worldwide, common in Africa, enter thru skin from water, mature in intestine or urinary bladder, snail-water- Human

TREMATODA

SCHISTOSOMES

Class Cestodia, Tapeworms • Highly specialized, endoparisites of digestive system • Lack mouth and digestive organs, absorb nutrients directly thru body wall, lost thru evolution • Long series of proglottids, each contains both male and female reproductive organs • Host maintains Homeostasis for worm

CESTODIA (TAPEWORM)

Eucestoda Tapeworms • Represent ultimate degree of specialization • Body divided into 3 regions • Scolex- holdfast structure contains circular suckers and sometimes hooks to anchor itself • Neck region narrows behind scolex • Strobilia- linear proglottids, reproductive units • Monoecious- each proglottid contains two complete sets of ovaries and testes, testes mature first, no cross fertilization • Beef , Pork and fish tapeworms common Human parasites

EUCESTODA

NEMERTEA

GASTROTRICHA

CYCLIOPHORA