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Download 6. Phylum - Nematoda
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Phylum Nematoda – Roundworms ACAD Body Plan •Bilateral symmetry •Long and slender unsegmented body that tapers at both ends •Protected by noncellular layer called a cuticle •Pseudocoelomates Copyright Pearson Prentice Hall Systems •One-way digestive tract with separate mouth and anus •Exchange gases, distribute nutrients, and excrete metabolic waste via diffusion through body walls Copyright Pearson Prentice Hall Feeding •Free-living roundworms use grasping mouthparts and spines to catch and eat other small animals •Many others are parasitic Copyright Pearson Prentice Hall Reproduction •Reproduce sexually •Most species have separate sexes •Parasitic roundworms often have life cycles that involve two or three different hosts or several organs within a single host Copyright Pearson Prentice Hall Parasitic Roundworms Groups Hookworms •Trichinella – get trichinosis by eating raw or incompletely cooked pork Copyright Pearson Prentice Hall Hookworm Life-cycle •Eggs hatch and develop in the soil •Use sharp toothlike plates and hooks to burrow into the skin and enter the bloodstream •Travel through the blood of their host to the lungs and down to the intestines •Suck the host’s blood, causing weakness and poor growth Copyright Pearson Prentice Hall Filarial Worms •Transmitted by mosquitoes •Causes Elephantiasis Copyright Pearson Prentice Hall Roundworms and Human Disease Ascaris – •serious parasite of humans and many other vertebrate animals •absorbs digested food from the host’s small intestine; makes host very sick Copyright Pearson Prentice Hall Ascarids Ascarids taken from children of one village. Copyright Pearson Prentice Hall Pinworms •Most common roundworm parasite in the United States – highly infectious •Do not cause serious disease Copyright Pearson Prentice Hall Phylum Rotifera – Rotifers Copyright Pearson Prentice Hall Rotifers •Pseudocoelomates •Transparent •Free-living and aquatic •Have a crown of cilia surrounding their mouth called a corona • The beating of the cilia sweeps food through their mouths into their digestive tract • Food moves through a one-way digestive tract as it is digested •Rotifers are capable of parthenogenesis – unfertilized eggs hatch into adults (all females) Copyright Pearson Prentice Hall
