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Nematoda Ubiquitous roundworms ph. Porifera ph. Cnidaria Protostome embryology Radial, diploblastic Bilateral, triploblastic sk. Parazoa sk. Eumetazoa asymmetrical, cellular level symmetrical, tissue level k. Animalia choanoflagellatelike ancestor Deuterostome embryology ph. Nematoda ph. Platyhelmitheyes Shed skin Don’t shed skin Protostome embryology Deuterostome embryology sk. Eumetazoa Figure 8-9 Phylum Nematoda • • • • • • Free-living or parasitic Most are very small, < 2mm But some are nearly 1m long Abundant (100’s in a cupful of soil) Diverse >20,000 named species, many others undescribed Nematode Body Design • • • • • • Cylindrical, pseudocoelomate Tough cuticle must be shed to grow Complete gut Only longitudinal muscles Usually diecious, sexes distinct But parenthogenesis is common C. elegans • Famous Nematode! • Cell lineage and origin known • Complete nervous “wiring diagram” • Genome sequenced Nematode adult anatomy Fig 15-10 Fig 15-11 Nematode Cuticle and Body Wall Cross Section Nematode Locomotion • Pressurized pseudocoelom holds shape • Longitudinal muscles that pull against that pressure to provide a spiral lashing motion • For burrowing and penetrating host tissues Nematodes • Feeding and Parasitism Feeding Modes of Nematodes • Microbivores – Select bacteria and fungi from soil and water • Predators – eat small prey, or pierce and suck out larger prey • Plant parasites • Animal parasites Nematode Diets and Mouths microbivore plant parasites predators Nematode Parasites of Animals • Intestinal parasites have simplified life cycles – Single host, direct re-infection • Blood parasites are transmitted by mosquitoes and other biting flies – Alternate hosts are also called vectors Ascaris Intestinal Roundworm (Ascaris) • genus Ascaris, females up to 30 cm • 67% used to be infected in S.E. United States • adults eat intestinal chyme • heavy infections cause abdominal pain and allergic reactions – or death, in heavy infections of children Ascaris Internal Migration • eggs transferred from feces to food or mouth by hand; hatch in intestine • larvae penetrate bloodstream, go to lungs • break out into alveoli and crawl up trachea to esophagus, swallowed again • adults live free in small intestine Dog Heartworm Life Cycle • Adult lives in dog’s heart muscle • releases eggs into bloodstream, which hatch into small larvae (“microfilariae”) • larvae enter a mosquito that bites the dog • enter another dog by mosquito’s next bite • migrate to heart and grow inside muscle Dog Heartworm Wucharia : Filarial worms Elephantiasis Live in lymphatic system; cause inflammation Microfilariae picked up by mosquitos – transmitted to new host Other Parasitic Nematodes • hookworm, pinworm, trichinosis, river blindness, etc. • cuticle protects against immune system and enzymes • can do without oxygen Hookworm: Necator Americanus Bloodfeeders, Cause anemia, feed on blood vessels in the intestinal mucosa Trichinella: Trichina worm Trichinosis – lethal, enter bloodstream thru intestinal veins And colonize many body tissues, under cooked meat Pinworm: Enterobius Adults live in intestine, females lay eggs at anus, infect new Host thru mouth and digestive system Pop Quiz! • 1.What type of body cavity and symmetry do flatworms have? • 2. Give the scientific name for each class of flatworm and an example of an organism in each. • How do parasitic flatworms feed?
