Phylum Nematoda

The Roundworms

Phylum Level Characteristics

• round, not flattened• no segmentation• complete digestive system

– (2 openings: mouth and anus)

• -soft bodied, hydrostatic skeleton• -bilateral symmetry• No circulatory system

– Nutrients and wastes diffuse through body cells

Nervous System

• Exhibit cephalization as they have a “head” end

• In head are several ganglia or nerve bundles, no real “brain”

• Have sense organs that detect chemicals given off by prey or hosts

• Longitudinal muscles so movement is “snake-like”

Reproduction

• Sexual

• Most species have separate males and females, a few are hermaphroditic

• Fertilization occurs within the female

• Parasitic life cycles can involve many hosts

Diversity

• most are free-living

• found in all habitats

• very successful (high # of species and large #’s of them)

Diversity

• parasitic round worms also infect most kinds of animals and plants

• -i.e. Ascaris infects

humans

Ascaris Life Cycle

• Adult worms live in intestines– Produce many eggs that leave in hosts feces

• Feces contaminated food or water eaten by another host– Eggs hatch in intestine of new host– Young worms burrow into the walls of the intestine

and enter surrounding blood vessels– Carried by blood, worms end up in lungs– Travel up air passage into throat then are swallowed– Carried back to intestines where process begins

again!ascaris animation

Diversity

• -i.e. hookworm can enter body through bare feet

Hookworm Life Cycle

• Hookworm eggs hatch and develop in soil• Use sharp teeth and hooks to burrow into feet• Continue burrowing until they enter the

bloodstream• Travel to lungs, coughed up and swallowed to

eventually reach intestines• Adult worms dig into intestinal wall and suck

blood of host

http://www.youtube.com/watch?v=tGHAlmCj3DM

Assignment:

1. Watch Nematoda video

2. Complete nematoda worksheet

3. Complete nematoda flash cards!

Please remind me that we need to catch up on the “ecological significance” notes for the last 2 phyla!!