Roundworms

Phylum Nematoda1. Nematodes: roundworms2. Nemata- “ thread”3. Bilateral symmetry4. Tube within a tube

structure-mouth and anus

5. 3 germ layers w/ pseudocoelom

6. Smaller than flatworms, taper at both ends

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PseudocoelomatePseudocoelomate

EctodermMesodermEndodermFluid filled cavity between the endoderm and ectoderm- pseudocoelom

Differs from a true coelom because…. • It is not entirely lined with mesoderm tissue• Organs are not suspended or attached to membranes

(mesenteries)

Lifestyle

1. Thick outer covering (cuticle) to protect them from harsh environment ex. Stomach acid

2. Move bodies with thrashing motion3. Free living-Decomposers and predators

(tremendously abundant)4. Parasitic- ex. Ascaris, hookworm,

heartworm-host is dog5. Sexually reproduce:

• most are separate sexes• some species are hermaphrodites

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Nematodes

Found everywhere Soil Oceans Polar ice Hot springs

Parasites of nearly all plant and animal species!

Body Systems No Respiratory or Circulatory Systems- limits

size of worm due to distribution of nutrients via osmosis and diffusion

Complete Digestive Nervous Muscular Excretory Reproductive

Digestive SystemComplete Digestive Tract- Mouth Pharynx Intestine anus

Muscular System Longitudinal muscles

only creates thrashing

movement

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Nervous System

Nerve ring – “brain”

Dorsal and

ventral nerve cords

Excretory System

Excretory cells Ducts pores

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Nematode Reproductive Systems

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Dioecious- separate sexes

Life cycles of parasitic roundworms ASCARIS

• lives in intestines and feeds off blood

• ingest eggs from dirty hands or unwashed veggies contaminated with fecal matter

• eggs hatch in intestines and enter bloodstream

• larval worms bore into lungs, must be coughed up and swallowed

• move to intestines where they mature

TRICHINELLA• bore into muscles causing

painful cysts or live in intestines

• ingest cysts in undercooked/raw meat (usually pork)

• cysts open up in intestines and reproduce there

• larvae move into muscle tissue and form cysts

HOOKWORMS

• lives in intestines • feeds on blood, causes

major damage to intestines• eggs deposited on soil from

contaminated wastes• larvae live in soil• burrow into feet or exposed

skin of host• larvae travel through

bloodstream, to lungs, coughed up, swallowed

• attach to intestinal wall where they mature

PINWORMS

• most commonly infects children

• lives in intestines• ingest eggs from

contaminated soil or sand

• hatch in intestines• female lays eggs near

anus at night causing severe itching

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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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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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Dirofilaria immitis

Dog heart worm

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The End