Zoology Exercise #10: Phylum Nematoda Lab Guide All animals with bilateral symmetry, except the acoelomates, have a body cavity. They are either true coelomates (where peritoneum covers both the inner surface of the body wall and outer surface of the organs) or pseudocoelomates (where the body cavity is not entirely lined with peritoneum. Pseudocoelomates tend to have a cylindrical body form, are un-segmented, and have a complete mouth to anus digestive tract. The epidermis is usually covered in a cuticle and they can be both aquatic and terrestrial (land dwelling). Nematodes are worldwide and can be terrestrial, freshwater, marine, and parasitic. They are covered in a flexible, non-living cuticle. Circular muscles are lacking and the group, Ascaris, the longitudinal muscles are arranged in four groups, separated by epidermal cords. Cilia are completely lacking. Ascaris lumbricoides is a common intestinal parasite in humans. Nearly one quarter of the human population is infected with Ascaris. Approximately 4 million people in the United States is infected with Ascaris. Infections are most common among immigrants, travelers, and refugees. Careless defecation near habitation by individuals harboring worms infect the soil with eggs that may remain infective for year. The eggs are very resistant to chemicals. Heavy infections can cause malnutrition in children with possible immune reactions. Some infections may lead to intestinal blockage and cause death. Exercise 10A Phylum Nematoda 1. Please describe the differences between the two types of body cavities all bilateral animals belong to. Also, explain how these are an advantage. 2. Discuss at least 3 unique attributes pertaining to the Genus Ascaris. 3. Discuss how common these parasites are in the United States, who they tend to infect, and how they manifest themselves in those infected.
Females are larger and more numerous than males. Males have a curved posterior end and two spicules made of chitin. These are used to hold the female s vulva open during copulation. The mouth will have 3 lips. There will be a ventral anus at the posterior end. In males the anus will discharge feces and act as the genital opening. The vulva (genital opening) in females is located on the ventral side about 1/3 down the length of her body. These animals have a shiny cuticle that is nonliving and made of collagen, which is also found in vertebrate connective tissue. Four longitudinal lines run the length of the body (dorsal & ventral are difficult to see on preserved specimens, but the two lateral lines are easier). The lateral lines appear somewhat transparent. Excretory canals are located inside the lateral lines. General Features (External Anatomy) SKETCH (Preserved Ascaris) LABEL Spicules (if yours is male) Mouth (w/3 lips) Anus Cuticle Vulva (female) Lateral lines 4. How was the sex of your specimen determined and if male, what were the spicules used for? 5. What is the cuticle made of and what tissue is it similar to in vertebrates? Procedure 1. Fill a dissecting pan with water and place a female specimen in the pan. 2. Now, locate the lateral lines, anus, and vulva. This will help you to determine the mid-dorsal line. 3. With a scalpel, slit the body wall along the mid-dorsal line, being VERY CAREFUL to avoid damaging the internal structures. 4. Begin to pin back the body wall as you expose the internal parts of the animal. ALWAYS slant you pins outward to avoid interfering with your view of the internal structures.
Excretory system: Excretory canals are located in the lateral lines and empty through an excretory pore. They act as osmoregulators. Excretion will also occur through the cuticle. Digestive system: The mouth empties into a short, muscular pharynx, which sucks food into its ribbon like intestine. The intestine is thin so it can absorb digested food. Digestion begins extracellularly and is completed intracellularly in cells of the intestinal wall. Respiratory/Circulatory systems: There are NO respiratory or circulatory structures. Oxygen is obtained mainly from the breakdown of glycogen within the body and distributed through the pseudocoel fluid. Reproductive system: The females reproductive system fills most of the pseudocoel. The system is a Y-shaped set of tubes. The short base of the Y is the vagina. It opens to the outside at the vulva. The long tubes of the inverted Y are the uteri. They extend to the posterior end and then double back as more slender, much-coiled oviducts. These terminate as thread-like ovaries. Eggs will pass from the ovaries through the oviducts to the uteri where fertilization will occur and shells will be secreted. The male reproductive system is essentially a single, long tube made up of a thread-like testes, which continues as a thicker vas deferens. The vas deferens connects with the wider seminal vesicles, which empty by a short, muscular ejaculatory duct in the anus. The males anus is often called a cloaca because it serves as an outlet for both the digestive and reproductive systems. The male will insert his spicules into the vulva of the female and discharge the spermatozoa into the vagina. Internal Structure of female Ascaris SKETCH (Female Ascaris) NOTE: You will not dissect a male, but be familiar with the structures LABEL Pharynx Intestine Anus Vagina Uteri Oviducts Ovaries
6. This packet mentions that the excretory canals are largely osmoregulatory. What does osmoregulatory mean? 7. How does excretion occur? 8. Explain how Ascaris obtains food and accomplishes digestion. 9. Explain how respiration and circulation are accomplished in Ascaris. 10. Describe the path the Ascaris eggs will take in the female s reproductive tract.
11. Describe the path sperm would take in the male s reproductive tract beginning with the testes. Procedure 1. Study the prepared stained transverse sections of Ascaris. Note the thick cuticle on the outside. Below this is the epidermis. Longitudinal muscles make up most the body as fluffy, irregular masses dipping into the pseudocoel. The tips will be nearest the nerve cords. Locate the dorsal and ventral nerve cords. The large uteri are filled with eggs enclosed in cells. The oviducts will also have eggs. The ovaries will appear wheel-shaped. The intestine is composed of a single layer of tall, column looking cells. The male cross section is similar to the female except for the rounded section of testes packed with spermatogonia which are the precursor to making functioning reproductive cells. There may be several sections of vas deferens containing spermatocytes and a possible section of a large seminal vesicle filled with mature spermatozoa. Transverse Section of Ascaris male & female on one slide SKETCH (Transverse Section male & female) LABEL Cuticle Epidermis Longitudinal muscles Pseudocoel Excretory canal Dorsal nerve cord Ventral nerve cord Uteri (female) Oviduct (female) Ovaries (female) Intestine Testes (male) Vas deferens (male)
Procedure 1. Place a drop of culture containing live Vinegar Eels on a clean microscope slide. 2. Examine with a light microscope. 3. Notice the thrashing movements of the worms. Because they have only longitudinal muscles, they can flex their bodies only from side of side. Note the blunt anterior end. Try to see the mouth, pharynx, and pharyngeal bulb. This will lead to a long, straight intestine, which ends at a ventral anus. 4. You may need to lower the light and ADD 1M HCl to slow the worms down enough to see these structures. Some Free-Living Nematodes -Turbatrix aceti Vinegar Eels SKETCH (Live Turbatrix aceti quieted using 1M HCl) LABEL Mouth Pharynx Pharyngeal bulb Intestine anus
12. Explain the mechanics of how the thrashing movement you observed in Turbatrix aceti occurs. (Use your textbook and/or screencast notes for help) Procedure 1. View prepared slides of Necator americanus (Hookworm) and Enterobius vermicularis (Pinworm) Other Parasitic Nematodes: Necator americanus Hookworm & Enterobius vermicularis & Pinworm SKETCH (Necator americanus Hookworm)
SKETCH (Enterobius vermicularis Pinworm) 13. Please discuss the life cycle of both the Hookworm and Pinworm using your textbook/screencast notes/ or any online resources. Also, discuss the symptoms one might experience if infected. LIFE CYCLE (Hookworm) SYMPTOMS (Hookworm) LIFE CYCLE (Pinworm) SYMPTOMS (Pinworm)