Module 6 Nematodes PDF

**ZOOL 1 -- General Zoology** **Objectives:** After the completion of the chapter, students will be able to: 1. Identify the distinguishing features of aschelminths 2. Distinguish between free -- living nematodes from parasitic nematodes 3. Know the different parasitic nematodes and thei...

**ZOOL 1 -- General Zoology** **Objectives:** After the completion of the chapter, students will be able to: 1. Identify the distinguishing features of aschelminths 2. Distinguish between free -- living nematodes from parasitic nematodes 3. Know the different parasitic nematodes and their mode of transmission. Phylum Nemathelminthes/ Nematoda/Nematodes  - Nematos- thread/ Askos- bladder, helminthes- worm - They are commonly called thread worm or round worm. - It is a phylum of unsegmented, triploblastic, pseudocoelomic, cylindrical or thread-like worms which are covered by a body wall having cuticle and epidermis. - Other zoologists consider Aschelminthes as a superphylum and its various groups as phyla (Rotifera, Gastrotricha, Kinorhynca, Nematomorph, Nematoda) - Phylum Nematoda is its large group. General characteristics**:** 1. Mostly parasitic. Few of them are free-living. 2. They are cylindrical, elongated, slender worm like and tapers at both end. 3. Triploblastic 4. Bilaterally symmetrical. 5. Organ system level of organization. 6. Body is unsegmented. 7. Body cavity is filled with muscle. 8. They are pseudocoelomate meaning, body cavity is not lined by mesodermal layer. 9. Internal cephalization is present but externally there is little differentiation between the anterior and posterior regions.\ Distinct head is lacking. However, mouth is present in anterior region. 10. Body is covered with tough and resistant cuticle 11. Digestive system is complete and straight with both mouth and anus. 12. Mouth is terminal and surrounded by lips bearing sense organ.  13. Respiratory and circulatory organs are absent.\ Respiration occurs through general body surface. Respiration is aerobic in free-living forms and anaerobic in parasitic form. 14. Excretory system consists of intracellular canal or lateral excretory ducts. (Renette cells) 15. Nervous system is not much developed. 16. Nervous system consists of circumpharyngeal nerve ring and longitudinal nerve cords*.* 17. Sense organs are poorly developed in the form of papillae, which are well defined as amphids (in mouth) and phasmid (in anus). 18. These are unisexual. Sexes are separate with sexual dimorphism. 19. Fertilization is internal, may be cross or self. 20. Development may be direct or indirect.\ NOTE: Larval* forms are Rhabditiform, Filariform and Micrifilaria.* 21. Various lateral lines and pores are present on the surface of body. **Ascaris lumbricoides**  **Filarial Worm** **Enterobius vermicularis**  **Loa Loa or African Eyeworm** **Ancylostoma duodenale**  **Trichuris trichiura**  **Things to Remember** - This is the** first unisexual** phylum. - The tail is often curved in male. - Amphids- are olfactory-receptors - Phasmids- are chemoreceptors and glandulo-sensory. - Resistant cuticle on the body surface is adaptation for its parasitic life. - Cuticle secreted by underlying epidermis is composed of scleroprotein. - No segmentation. In some, the cuticle is striated and thus giving the appearance of segmentation and called pseudo-segmentation. - The pharynx is triradiate. - Males are usually smaller than females. - During development volume of cell increases (no increase in number of cells). Ascaris lumbricoides - Monogenetic life cycle, found in small intestine (jejunum) of man. - Cause Ascariasis. - Male Ascaris are monarchic or monodelphic (presence of single testis). - Female are diorchic or didelphic (presence of pair of ovaries). - In Ascaris, fertilization occurs in uterus. - Moulting in life cycle occurs four times: - 1^st^ moulting- in soil - 2^nd^ and 3^rd^ moulting- in lungs - 4^th^ moulting- in intestine.\ 2^nd^ stage larva enters the lungs and 4^th^ stage larva comes out of the lungs. - Excretory organ is H-shaped. - Mode of transmission- contaminated food and water. - Infective stage- embryonated eggs with rhabditiform larva.