1. Stage 4: Internal Body Cavity
Phyla Nematoda

2. A. The Roundworms
1. These organisms… a. have a cavity positioned between the mesoderm and endoderm. b. have an opening to the gut on both ends (mouth and anus). 2. Taxonomy a. Phylum Nematoda b. 20,000 species (The most numerous organisms on the planet.)

3. B. Structure and Function
1. Body form and function:
a. Tube-like bodies that are
tapered at both ends.
b. Pseudocoelum
(1) Open cavity.
(2) Between the mesoderm and endoderm.
(3) This change allows for:
(a) Circulation: fluids move freely in body cavity.
(b) Movement: fluid in body cavity causes body to be rigid and offers resistance for muscles to work against.
(c)Organ Function: organs are cushioned against being crushed by muscles.

4. C. Niche
1. Adapted to every habitat. 2. Free living- a. Tiny dwellers in substrate (meiofauna). b. one-square meter of bottom mud can contain up to 4.4 million nematodes. 3. Parasitic a. One of the most common phyla of parasitic infection. b. Heartworm, hookworm and pinworm.

5. D. Showcase System: Digestive
1. Complete digestive tract present for the first time.
a. Tract – group of organs that run throughout the body.
b. lips  mouth  pharynx  intestine anus
2. Digestion takes place in the organs using enzymes to breakdown food. Molecular nutrients are absorbed from the intestine through the body.

6. E. Strange but true!
1. The nematode C. elegans is one of the most widely studied animals on the planet. 2. Its simple structure and rapid rate of reproduction make it an ideal organism for genetic research.

7. Got Parasites?