Chp 11

• Class Aphasmida


  Without phasmids (caudal sensory organs), excretory system is absent or reduced, male with one spicule or the spicule is lacking
• Order Trichurida


  1. The anterior end of the worm is more slender than the posterior end

  2. The esophagus possesses one or two rows of gland cells called stichocytes along its posterior portion

  3. The excretory system is absent

  4. Related to the intestine are glandular and non-glandular cells known as bacillary bands

  5. The glandular cells may have a role in ion and osmotic regulation, and the non-glandular cells in cuticle formation and food storage

  
• Trichinella spiralis


  • A parasite of mammals including humans
  • The immature and adult stages may be found in the same host
  • The esophagus occupies ⅓ - ⅟2 of body length
  • The male lacks spicule but the body ends by a copulatory pseudobursa

  
• Life cycle of Trichinella spiralis

  1. The adult lives in the intestinal wall, by ovoviviparity, it gives juveniles that move with blood circulation throughout the body

  2. In skeletal muscles, the juvenile becomes encysted

  3. Human is infected when he consumes pork flesh infested with these cysts

  4. The infection causes fever, diarrhea and damage of blood vessels and infected organs during its migration

  5. The stichocytes secretion alters the function of muscle nurse cells that nourish the worm, the nuclei hypertrophy and myofibrils are lost

  
• Class Phasmida


  • With phasmids and developed excretory system
  • The male possesses one or two spicules
• Order Oxyurida


  1. The posterior body region is modified as sharply pointed tail

  2. The esophagus has a posterior bulb

  3. The male is haploid, the female is diploid

  4. They are parasitic in the large intestine and rectum of vertebrates, and the rectum of some invertebrates mainly arthropods
• Enterobius vermicularis


  • A parasite in the colon and rectum of human
  • The male has a single spicule

  
• Life cycle of Enterobius vermicularis

  1. The worms migrate along the entire digestive system

  2. At night, they migrate to the perianal skin, lay eggs and die

  3. If the egg stays for a long period, they hatch and cause a retroinfection, but usually the infection occurs through contaminated food or water with worm's eggs

  4. The infection causes irritation, mucosal ulceration and secondary bacterial infection