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CHAPTER 18 The Ecdysozoas Phylum Nematoda 18-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nematode: Trichinella 18-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diversity Many protostomes possess a cuticle 18-3 Non-living outer layer secreted by epidermis Cuticle restricts growth and must be molted via ecdysis (shedding) Members of Ecdysozoa molt cuticle as they grow Regulation of molting achieved by the hormone ecdysone Nematodes are known as Small Ecdysozoans Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diversity Nematoda (Roundworms) are Pseudocoelomate Flatworms = acoelomates Diversity About 25,000 species are described Found in virtually all habitats in all biomes 18-5 As many as half a million may exist Topsoil may contain billions per acre Nematode parasites exist in nearly all animal and plant species Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms 18-6 Free-living nematodes feed on bacteria, yeasts, fungal hyphae, and algae Predatory nematodes eat rotifers, tardigrades, small annelids, and other nematodes Nematodes are food for mites, insects, larvae, and fungi Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Form and Function Distinguishing Characteristics Cylindrical shape Nonliving cuticle Cuticle shed during juvenile growth stages superphylum Ecdysozoa Lack motile cilia or flagella Longitudinal muscles in body wall 18-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Female Ascaris (Roundworm) 18-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Digestion Alimentary canal consists of mouth, pharynx, nonmuscular intestine, short rectum and anus Pharynx sucks food in Intestinal wall is one cell thick 18-9 Food moves back as new food enters and the body moves Mouth and Anus = Complete Gut Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Ring of nerve tissue and ganglia around the pharynx lead to dorsal and ventral nerve cords Sensory organs at head and tail Amphids = chemoreceptors near anterior end Parasitic nematodes have a bilateral pair of phasmids near posterior end that resemble amphids Most are dioecious with males smaller than females Fertilization is internal Eggs are stored in uterus until deposited Cuticle is shed between each of four juvenile stages 18-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Amphid (chemoreceptors in Anterior region) 18-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Representative Nematode Parasites Some are parasites of humans Most are tropical Ascaris lumbricoides 18-12 Occurs in up to 25% of people in some areas of the southeastern U.S. More than 1.27 billion affected worldwide 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 Embryos develop into juveniles in 2 weeks Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Male and Female Ascaris Roundworm Male is smaller (top), Female is larger 18-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms 18-14 Viable eggs remain after signs of fecal matter have disappeared Survive for long periods in soil 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 Coughed up and swallowed, they mature in the intestine after two months They feed on intestinal contents and may block or perforate the intestines Infection rates tend to be higher in children and males Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Life Cycle of Ascaris Roundworm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Hookworms Anterior end of these small (9–11 mm) worms has a hook-like curve Necator americanus, most common hookworm. Sexes are separate Large plates in mouth cut into intestinal wall and suck host’s blood Pump through more blood than they digest 18-16 Heavy infections cause anemia 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 Travel in blood to the lungs, are coughed up to be swallowed, and mature in the intestine 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 18-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life cycle of Hookworm 18-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Trichina Worm Trichinella spiralis causes a potentially lethal trichinosis 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 Penetrate skeletal muscle cells 18-19 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 Heavy infection in mammals causes death Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Muscle infected with Trichina worm 18-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Pinworms 18-21 Most common worm parasite in the U.S. but causes little disease Adults live in large intestine Females, about 12 mm long, migrate to anal region at night and lay eggs, causing itching Scratching the anal region contaminates hands and bedclothes Eggs develop rapidly and become infective within six hours at body temperature When swallowed, hatch in duodenum and mature in large intestine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A.Female pinworm from intestine B.Group of Pinworm eggs released from anus 18-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Filarial Worms Eight species of filarial nematodes infect humans Some cause serious diseases Wucheria bancrofti and Brugia malayi live in lymphatic system Cause inflammation and blockage of the lymphatics vessels Females release live young, tiny microfilariae, into blood and lymph Mosquitoes ingest microfilariae when they feed Worms develop to infective stage and move into the mosquito bite wound when it feeds Elephantiasis is caused by repeated exposure 18-23 Swelling and growth of connective tissue causes enormous swelling of body parts Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms 18-24 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle of Filarial Worm Wuchereria bancrofti 18-25