Phylum Nemata:

The Round-worms

What’s a Nematode?• Nematodes are different from more familiar

worms (such as the earthworm) because they have no body segments. Hence the name “round” worm

Roundworm (Nematode)

Segmented Worm (Annelid)

So What’s Different from Flatworms?• Anus• Pseudocoelum (body cavity)– The psudocoelum allows for the distribution of nutrients and oxygen to

all of a nematode’s cells.

Flatworm:No Pseudocoelum

Other Nematode Characteristics

• Triploblastic (Ectoderm, endoderm, and mesoderm.

• Digestive system with mouth & anus.• Hard cuticle similar to an exoskeleton• Sexual reproduction (usually)

Nematode Anatomy

• “Tube within a tube” body plan

Many species• There are many thousands, perhaps even

500,000 different nematode species on Earth, making them the 2nd most successful animal phylum by this measure.

• They can be found in soil, marine, and freshwater environments on every continent.

• Some species are free-living and others are parasitic

Life Cycle: Egg, Larva, Adult, repeat

Roundworm Ecology

• Roundworms are an important part of the soil ecosystem:– 1 g of soil may contain hundreds of nematodes!– Different species eat different things, sometimes

even other nematodes.– Many are beneficial because they infect the larvae

of damaging insects.– Some infect plants.

Bad Nematodes: Heartworm• Heartworm is a common infection of household

pets, especially dogs.• Spread by mosquito bites

Bad nematodes: Loa Loa (African Eye Worm)

• Rare outside of Congo and Sudan, but spectacularly disgusting. May cause blindness.

• Spread by biting flies

Bad Nematode: Intestinal Roundworm

• Infected dog intestines pictured. Some species can infect humans