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Phylum Nematoda

Adapted by Tamara Lookabaugh from

BIO 2215

Oklahoma City Community College

Dennis Anderson

Special Characteristic

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Pseudocoelomates – very little cavity but improved over acoelomates

1. greater freedom of movement2. space for development of organ systems3. a simple circulatory system4. storage for wastes5. hydrostatic organ

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General Characteristics25,000 species 500,000 predicted

1. Bilateral symmetry

2. Only longitudinal muscles

3. No segmentation

4. Pseudocoelomate

5. Separate sexes

6. Internal fertilization

7. 3 germ layers

8. Complete digestive system

9. No circulatory or respiratory system

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Habitats of Nematodes

• Found everywhere-free-living and parasitic– Moist Soil– Oceans (Deep Marine)– Polar ice caps– Hot springs– Parasites of nearly all plant

and animal species!– Parasites of nearly every

body or organ system

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MyxozoaMyxozoaMyxozoaMyxozoa

ArthropodaArthropodaArthropodaArthropoda AnnelidaAnnelidaAnnelidaAnnelida

MolluscaMolluscaMolluscaMollusca

LophophoresLophophoresLophophoresLophophores

HemichordataHemichordataHemichordataHemichordata

ChordataChordataChordataChordata

Other Other pseudocoelomatespseudocoelomates

Other Other pseudocoelomatespseudocoelomates

NematodaNematodaNematodaNematoda

PoriferaPoriferaPoriferaPorifera

CtenophoraCtenophoraCtenophoraCtenophoraCnidariaCnidariaCnidariaCnidaria

PlacozoaPlacozoaPlacozoaPlacozoa

PlatyhelminthesPlatyhelminthesPlatyhelminthesPlatyhelminthesNemerteaNemerteaNemerteaNemertea

CiliophoraCiliophoraCiliophoraCiliophoraSarcomastigophoraSarcomastigophoraSarcomastigophoraSarcomastigophora

MicrosporaMicrosporaMicrosporaMicrosporaApicomplexaApicomplexaApicomplexaApicomplexa

MesozoaMesozoaMesozoaMesozoa

EchinodermataEchinodermataEchinodermataEchinodermata

CrustaceaCrustaceaCrustaceaCrustaceaChelicerataChelicerataChelicerataChelicerata

UniramiaUniramiaUniramiaUniramia

Other ChordataOther ChordataOther ChordataOther Chordata

Two Classes of Nematodes

Class Phasmidia

• All worms in this group have PHASMIDS which are a type of sensory structure found in the posterior end of these worms.

Class Aphasmidia

• Worms in this group have no phasmids or they are VERY REDUCED in size.

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Integumentary System

• Cylindrical in Shape with Hollow pseudocoel

• High osmotic pressure within

• Thick cuticle is secreted by epidermis and allows the Nematodes to live so many places.

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Digestive System• Straight tube that lacks

muscles except at mouth, pharynx and rectum(anus)

• Some are carnivorous and have well developed jaws and teeth

• Some are scavengers, parasites or bacteria feeders with simple mouthparts

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Circulation and Gas Exchange

• Gas and food move around inside by body movements

• Diffusion is how gas and food move throughout

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Nervous System

• Dorsal, Lateral, Ventral Cords leading from a central ganglia nerve center

• Setae and papillae are mechanical sense receptors

• Amphids are chemical sensory receptors(Usually found in the head region)

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Dorsal and Ventral Nerve Cords

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Reproduction of Nematodes

Separate Sexes = Dioecious

Reproduction

• No larval stages

• Juveniles are small and sexually immature

• Four stages to get from young to adult

• Molt 4 times = shed cuticle

• Internal fertilization – females lay eggs or give birth to juveniles

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Nematode Reproductive Systems

Class Phasmidia

• GENERAL INFO– Free-living in freshwater or soil/parasitic– Many aid in aerating soil– Males smaller/females curved posterior– Many feed on crops and plants (pests)

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Phasmid Examples

1. Ascaris lumbricoides

2. Necator americanus

3. Enterobius vermicularia

4. Filarial worms

5. Caenorhabitis elegans (C. elegans)

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Ascaris lumbricoides

• Intestinal roundworm of man• 1.2 billion people worldwide,

– 64% of people in Southeastern US– Extensively studied in research

• Females lay 200,000 eggs a day• Found in unsanitary habitats and eating

uncooked veggies• Infection highest in children – especially eating

dirt• Rarely fatal, but can be if intestine blocked

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

Source: Redrawn From Centers for Disease Control, Atlanta, GA.

Life Cycle of Ascaris Lumbricoides

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Hookworms• Anterior end hooks• Examples ARE• Necator americanus• Ancylostoma duodenale

& caninum• Feed on blood/burrow

through skin• Cause anemia or protein

deficiencies• Common in tropical

regions warm moist soil

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

Life Cycle of Necator Americanus

Source: Redrawn From Centers for Disease Control, Atlanta, GA.

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Ancylostoma caninum

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Cutaneous Larval Migrans

• Hookworms from dogs and cats

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Enterobius vermicularis

“Pin worm”•Most common infection in U.S.

30% children,

16% adults,

30% college students•Spread

– Fecal oral route – irritation of anus when lay eggs, rub off on sheets

– Airborne eggs infective within 6 hours– Worms mature and live in large intestine– Diagnosis by Scotch Tape Method

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Life Cycle of Enterobius Vermicularis

Source: Redrawn From Centers for Disease Control, Atlanta, GA.

Filarial Worms

• Blood and Lymph Parasites

• Block lymph passageways = Elephantitis

• Females release live young “microfilariae” that are spread by mosquitoes or other insects

Examples:•Diorofilaria immitis•Wucheria bancrofti•Brugia•Loa loa•Dracunculus medinesis

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Dirofilaria immitis

• Dog heart worm

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Wuchereria bancrofti

• Lives in lymphatic system

• Obstruct lymph to cause swelling– Elephantiasis

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Elephantiasis

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

Source: Redrawn From Centers for Disease Control, Atlanta, GA.

Fig. 11.15

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Life Cycle of Wucheria spp.

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Loa loa• Eye worm

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Dracunculus medinesis• Fiery serpent

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Caenorhabditis elegans• Free living nematode• Eutely

– Constant number of cells

• 959 cells– Development of every

cell is known

• Genome sequenced• Compare genomes

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Nobel Prize for Worms

• Sydney Brenner– C. elegans since 1963

• Brenner, Sulston and Horwite awarded Nobel Prize in 2002

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Class AphasmidiaTrichinella spiralis

• Trichina worm• Freshwater and marine

environments• Carnivores like: Pigs,

bear, dogs, cats, rats and man

• Trichinosis (raw meat)– Encysts in muscles

causes cells to LOSE striations that become nurse cells for the worm.

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

Source: (a) Redrawn From Centers for Disease Control, Atlanta, GA. (b) Photo © Steve Miller

Life Cycle of Trichinella Spiralis

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The End