1. Phylum Nematoda

2. I. Phylum Nematoda
The Nematodes, also known as the ROUNDWORMS are one of the most ABUNDANT animals on earth. There have been nearly 16,000 species described already with possibly tens-of-thousands yet to be discovered.

3. I. Phylum Nematoda
They have been grouped along with 7 other phyla for the similar body structures into a larger group called the ASCHELMINTHS. Their evolutionary descent is UNCLEAR, but all the aschelminths have similar body cavities. They are considered to be PSEUDOCOELOMATES because their body cavity is not fully lined with a mesoderm. They also are lacking MESENTARIES, linings and membranes that are used to SECURE the INTERNAL ORGANS.

4. II. Characteristics of the Phylum Nematoda
a. TRIPLOBLASTIC, bilateral, VERMIFORM (resembling a WORM shape), UNSEGMENTED, pseudocoelomates, mild cephalization with primitive BRAIN
b. Body is ROUND in cross section and covered in a CUTICLE

5. II. Characteristics of the Phylum Nematoda
a. COMPLETE digestive system, mouth usually surrounded by lips bearing sense organs
b. Excretory system composed of RENETTE cells. Have no BLOOD or GAS EXCHANGE systems.
c. Body wall has only LONGITUDINAL muscles

6. III. External Features
The nematode body form is VERMIFORM. That is, that it resembles a WORM. It is elongated, slender, cylindrical and tapered at both ends.

7. a. The CUTICLE:
a NONCELLULAR, protective, organic layers secreted by the external epidermis. The cuticle may be smooth or contain spines, bristles, and ridges. It also is used for protection in parasitic nematodes because it is resistant to DIGESTION.

8. b. The EPIDERMIS
: a.k.a. the hypodermis, secretes the CUTICLE. The epidermis contains four major cords; one DORSAL, one VENTRAL, and two LATERAL cords that project inward. The dorsal and ventral cords are NERVE cords where the lateral cords are EXCRETORY in nature.

9. c. The LONGITUDINAL MUSCLES
The LONGITUDINAL MUSCLES: the principal means of LOCOMOTION in nematodes. The contraction of these muscles result in undulated waves that pass from the anterior to posterior end of the animal. This gives the round worms their characteristic THRASHING movements. Because they lack CIRCULAR MUSCLES they are unable to CRAWL like other worms.

10. d. The SENSORY ORGANS: the nematodes contain two main sensory organs.
i. AMPHIDS: ANTERIOR depressions in the CUTICLE that contain CHEMORECEPTORS.
ii. PHASMIDS: POSTERIOR CHEMORECEPTORS near the ANUS

11. IV. Internal Features:
The nematode pseudocoelom is a spacious, FLUID FILLED cavity that contains the visceral organs and forms a HYDROSTATIC skeleton. What does hydrostatic mean?

12. a. Feeding and Digestion: Nematodes feed on any source of ORGANIC matter whether living or dead. They play an important role in the processing of SOIL and some cause CROP DISEASES. Therefore they are highly studied for their AGRICULTURAL IMPACT

13. i. COMPLETE DIGESTIVE SYSTEM: Nematodes have a TUBULAR digestive tract that extends from the anterior mouth to the posterior anus with a muscular PHARYNX that moves the food through the system. This is the first time that organisms have been able to take in food, DIGEST it, ABSORB its nutrients, and PASS it out as feces in one SEQUENTIAL motion. This is a huge advantage to the nematodes and high order organisms.

14. EXCRETORY SYSTEM: The nematodes have a WASTE management system that is made of VENTRAL glandular cells called RENETTES

15. NERVOUS SYSTEM: Nematodes have an ANTERIOR primitive brain called a NERVE RING. Nerves extend both anteriorly and posteriorly

16. REPRODUCIVE SYSTEM: Most nematodes are DIOECIOUS and DIMORPHIC, with the MALES being SMALLER than the FEMALES. The males can be identified by a CURLED posterior end

17. Important Nematode Parasites of Humans
ASCARIS: The GIANT INTESTINAL ROUNDWORM causes the disease ASCARIASIS which can result in the blockage of the intestines. (tickle in the throat)

18. b. ENTEROBIUS: The HUMAN PINWORM does not cause any major problems to the human body apart from intense ANAL ITCHING when the females crawl out of the anus to lay eggs.

19. TRICHINELLA: The PORKWORM causes the disease TRICHINOSIS
TRICHINELLA: The PORKWORM causes the disease TRICHINOSIS. Which can result in nausea, heartburn, diarrhea, headaches, cramps, etc. trichinosis is very rare in the U.S.

20. WUCHERERIA: The FILARIAL Worm is transmitted by MOSQUITOS and causes ELEPHANTIASIS which results in the enlargement of various appendages due to the blockage of the LYMPH SYSTEM. In the U.S. filarial worms are more commonly found in dogs and known as HEARTWORMS. Heartworm disease can be fatal in dogs.

21. Hungry???

22. In the News… “British Researchers Create Human-Animal Hybrid Embryos”
Ethics?
Why?
Predict the Future…Good and Bad.

23. Earthworm observation
Place an earthworm in your hand.
How does the bottom feel as it crawls on you?
What structures are you feeling?
Locate the Clitellum.
What is the function of the clitellum?
On the surface of the body are openings for the excretory and reproductive system. Using a dissecting microscope, locate the seminal receptacles and the oviducts.
What are the functions of these pores?