18-1 CHAPTER 18 The Ecdysozoas Phylum Nematoda The Ecdysozoas Phylum Nematoda

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nematode: Trichinella

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Diversity Many protostomes possess a cuticle Many protostomes possess a cuticle Non-living outer layer secreted by epidermis Non-living outer layer secreted by epidermis Cuticle restricts growth and must be molted via ecdysis (shedding) Cuticle restricts growth and must be molted via ecdysis (shedding) Members of Ecdysozoa molt cuticle as they grow Members of Ecdysozoa molt cuticle as they grow Regulation of molting achieved by the hormone ecdysone Regulation of molting achieved by the hormone ecdysone Nematodes are known as Small Ecdysozoans Nematodes are known as Small Ecdysozoans

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nematoda (Roundworms) are Pseudocoelomate Nematoda (Roundworms) are Pseudocoelomate Flatworms = acoelomates Flatworms = acoelomatesDiversity About 25,000 species are described About 25,000 species are described As many as half a million may exist As many as half a million may exist Found in virtually all habitats in all biomes Found in virtually all habitats in all biomes Topsoil may contain billions per acre Topsoil may contain billions per acre Nematode parasites exist in nearly all animal and plant species Nematode parasites exist in nearly all animal and plant species Diversity

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Free-living nematodes feed on bacteria, yeasts, fungal hyphae, and algae Free-living nematodes feed on bacteria, yeasts, fungal hyphae, and algae Predatory nematodes eat rotifers, tardigrades, small annelids, and other nematodes Predatory nematodes eat rotifers, tardigrades, small annelids, and other nematodes Nematodes are food for mites, insects, larvae, and fungi Nematodes are food for mites, insects, larvae, and fungi Phylum Nematoda: Roundworms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Form and Function Distinguishing Characteristics Distinguishing Characteristics Cylindrical shape Cylindrical shape Nonliving cuticle Nonliving cuticle Cuticle shed during juvenile growth stages Cuticle shed during juvenile growth stages superphylum Ecdysozoa superphylum Ecdysozoa Lack motile cilia or flagella Lack motile cilia or flagella Longitudinal muscles in body wall Longitudinal muscles in body wall Phylum Nematoda: Roundworms

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Digestion Digestion Alimentary canal consists of mouth, pharynx, non- muscular intestine, short rectum and anus Alimentary canal consists of mouth, pharynx, non- muscular intestine, short rectum and anus Pharynx sucks food in Pharynx sucks food in Intestinal wall is one cell thick Intestinal wall is one cell thick Food moves back as new food enters and the body moves Food moves back as new food enters and the body moves Mouth and Anus = Complete Gut Mouth and Anus = Complete Gut Phylum Nematoda: Roundworms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Ring of nerve tissue and ganglia around the pharynx lead to dorsal and ventral nerve cords Ring of nerve tissue and ganglia around the pharynx lead to dorsal and ventral nerve cords Sensory organs at head and tail Sensory organs at head and tail Amphids = chemoreceptors near anterior end Amphids = chemoreceptors near anterior end Parasitic nematodes have a bilateral pair of phasmids near posterior end that resemble amphids Parasitic nematodes have a bilateral pair of phasmids near posterior end that resemble amphids Most are dioecious with males smaller than females Most are dioecious with males smaller than females Fertilization is internal Fertilization is internal Eggs are stored in uterus until deposited Eggs are stored in uterus until deposited Cuticle is shed between each of four juvenile stages Cuticle is shed between each of four juvenile stages Phylum Nematoda: Roundworms

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Representative Nematode Parasites Some are parasites of humans Some are parasites of humans Most are tropical Most are tropical Ascaris lumbricoides Ascaris lumbricoides Occurs in up to 25% of people in some areas of the southeastern U.S. Occurs in up to 25% of people in some areas of the southeastern U.S. More than 1.27 billion affected worldwide More than 1.27 billion affected worldwide Some species of Ascaris is found in the intestine of horse and pigs. Some species of Ascaris is found in the intestine of horse and pigs. A female Ascaris may lay 200,000 eggs a day, which pass out in host’s feces A female Ascaris may lay 200,000 eggs a day, which pass out in host’s feces Embryos develop into juveniles in 2 weeks Embryos develop into juveniles in 2 weeks Phylum Nematoda: Roundworms

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Viable eggs remain after signs of fecal matter have disappeared Viable eggs remain after signs of fecal matter have disappeared Survive for long periods in soil Survive for long periods in soil Host swallows embryonated eggs, juveniles hatch, and burrow through intestinal wall Host swallows embryonated eggs, juveniles hatch, and burrow through intestinal wall Carried through the heart to the lungs, they break into alveoli and are carried up to tracheae Carried through the heart to the lungs, they break into alveoli and are carried up to tracheae Coughed up and swallowed, they mature in the intestine after two months Coughed up and swallowed, they mature in the intestine after two months They feed on intestinal contents and may block or perforate the intestines They feed on intestinal contents and may block or perforate the intestines Infection rates tend to be higher in children and males Infection rates tend to be higher in children and males Phylum Nematoda: Roundworms

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hookworms Hookworms Anterior end of these small (9–11 mm) worms has a hook-like curve Anterior end of these small (9–11 mm) worms has a hook-like curve Necator americanus, most common hookworm. Necator americanus, most common hookworm. Sexes are separate Sexes are separate Large plates in mouth cut into intestinal wall and suck host’s blood Large plates in mouth cut into intestinal wall and suck host’s blood Pump through more blood than they digest Pump through more blood than they digest Heavy infections cause anemia Heavy infections cause anemia Eggs pass out in feces and juveniles hatch in soil Eggs pass out in feces and juveniles hatch in soil If human skin comes in contact with soil, infective juveniles burrow through skin to blood If human skin comes in contact with soil, infective juveniles burrow through skin to blood Travel in blood to the lungs, are coughed up to be swallowed, and mature in the intestine Travel in blood to the lungs, are coughed up to be swallowed, and mature in the intestine Phylum Nematoda: Roundworms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hookworm: A. Mouth showing cutting plates B. Hookworm attached to dog intestine, cutting plates pinch of intestine wall Hookworm secretes an anticoagulant to prevent blood from clotting

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Trichina Worm Trichina Worm Trichinella spiralis causes a potentially lethal trichinosis Trichinella spiralis causes a potentially lethal trichinosis Adult worms burrow into intestinal wall and females directly produce juvenile worms Adult worms burrow into intestinal wall and females directly produce juvenile worms Juveniles penetrate blood vessels and circulate throughout the body to all tissues and spaces Juveniles penetrate blood vessels and circulate throughout the body to all tissues and spaces Penetrate skeletal muscle cells Penetrate skeletal muscle cells Cells lose striations and becomes a nurse cells (continues to nourish) to the parasite Cells lose striations and becomes a nurse cells (continues to nourish) to the parasite When poorly cooked meat containing encysted juveniles is eaten, worms are liberated and mature in the intestine When poorly cooked meat containing encysted juveniles is eaten, worms are liberated and mature in the intestine Heavy infection in mammals causes death Heavy infection in mammals causes death Phylum Nematoda: Roundworms

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Pinworms Pinworms Most common worm parasite in the U.S. but causes little disease Most common worm parasite in the U.S. but causes little disease Adults live in large intestine Adults live in large intestine Females, about 12 mm long, migrate to anal region at night and lay eggs, causing itching Females, about 12 mm long, migrate to anal region at night and lay eggs, causing itching Scratching the anal region contaminates hands and bedclothes Scratching the anal region contaminates hands and bedclothes Eggs develop rapidly and become infective within six hours at body temperature Eggs develop rapidly and become infective within six hours at body temperature When swallowed, hatch in duodenum and mature in large intestine When swallowed, hatch in duodenum and mature in large intestine Phylum Nematoda: Roundworms

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Filarial Worms Filarial Worms Eight species of filarial nematodes infect humans Eight species of filarial nematodes infect humans Some cause serious diseases Some cause serious diseases Wucheria bancrofti and Brugia malayi live in lymphatic system Wucheria bancrofti and Brugia malayi live in lymphatic system Cause inflammation and blockage of the lymphatics vessels Cause inflammation and blockage of the lymphatics vessels Females release live young, tiny microfilariae, into blood and lymph Females release live young, tiny microfilariae, into blood and lymph Mosquitoes ingest microfilariae when they feed Mosquitoes ingest microfilariae when they feed Worms develop to infective stage and move into the mosquito bite wound when it feeds Worms develop to infective stage and move into the mosquito bite wound when it feeds Elephantiasis is caused by repeated exposure Elephantiasis is caused by repeated exposure Swelling and growth of connective tissue causes enormous swelling of body parts Swelling and growth of connective tissue causes enormous swelling of body parts Phylum Nematoda: Roundworms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display River blindness or onchocerciasis is carried by black flies and infects 37 million people in tropics River blindness or onchocerciasis is carried by black flies and infects 37 million people in tropics Dog heartworm, Dirofilaria immitis, is carried by mosquitoes and is the most common U.S. filarial worm Dog heartworm, Dirofilaria immitis, is carried by mosquitoes and is the most common U.S. filarial worm Phylum Nematoda: Roundworms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Life Cycle of Filarial Worm Wuchereria bancrofti