Nematoda

1. Nematoda By: John Lee, Jon Fuller, and Vicky Hung

2. Phylum & Sample Animals • Phylum: Nematoda • Classes: Adenophorea, Secernentea • Sample Animals: • Caernorhabditis Elegans • Involves in aging in human • It’s a model organism for research • Trichinella Spiralis • Acquired by ingesting infected pork • Develop along the intestinal muscles • Invades muscle cells and control it.

3. Body Cavity • Pseudocoelom: It has a body cavity only partially lined by tissue derived from mesoderm.

4. Body Symmetry • Radial Symmetry. • Any imaginary slice through the central axis divides the animal into mirror images. • They have no head or read end, no left and right side.

5. Nervous System • Nematodes have a simple nervous system, with a main ventral nerve cord and a smaller dorsal nerve cord. http://www.absoluteastronomy.com/topics/Nematode

6. Circulatory System • There is no circulatory system

7. Digestive System • Nematodes have a digestive system which includes separate sites for food intake. • The system is divided into three parts: stomodeum, intestine, and proctodeum. • The stomodeum consists of the esophagus, the “mouth” and “lips”, and buccal cavity. http://nematode.unl.edu/digestive_system.html

8. Excretory System • Simple and tubular with no cilia/flagella. • Consists of one or two single celled glands called renette cells • Functions: (1) excretion of metabolic waste, (2) Osmoregulation, (3) secretion and export of hormones to target tissues, http://www.infoplease.com/ce6/sci/A0835177.html

9. Locomotion/musculature • Movement due to longitudinal muscles that when contracted produced a thrashing motion.

10. Skeletal Type • Nematodes have a hydrostatic skeleton. • The pressure from the pseudocoelom and the muscles change an organism’s shape and produce movement. http://www.ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html

11. Sensory Structure • Nematodes have amphids, and phasmids. • Amphids are on the anterior. • Phasmids are on the posterior end. http://www.ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html

12. Reproductive system • Reproduction is usually sexual. • Involves internal fertilization. • Female may deposit 100,000 or more fertilized eggs per day. • Zygotes are resistant cells and can survive harsh conditions. • Females are larger than males

13. Gas Exchange • Gas exchange occurs through diffusion. • Some parasitic nematodes have a form of hemoglobin in the body fluids. • Anaerobic and Aerobic metabolism is also common. http://entomology.ifas.ufl.edu/creatures/nematode/marine_nematodes.htm

14. Unique Features • Trichinella (a type of nematode) has been dubbed “animals that act as viruses” because they invade muscle cells and control genes which code for proteins which make cellselastic enough to house nematodes. • The Cuticle which is a hard exterior that the worm sheds and excretes as it grows. • Blastula • Resulting from the folding of the mesoderm. • Protosome

15. Questions • How do the nematoda use there musculature for motion differently from the others? • What is the skeletal system called? What does this mean? • Why are some nematodes called “animals that act like viruses”? • Which type of symmetry do nematodes exhibit? How can you tell?

16. Answers • Nematoda have longitudinal muscles that they contract rapidly and create a thrashing motion. • They have hydrostatic skeletal systems that react to the environment and the pressure that is exerted upon them • Some have learned to control the muscles of humans in order to receive the nutrients they need to survive. • The nematodes have radial symmetry that can be proven by the fact that they can be cut anyway through the central axis to create mirror images.