Understanding Pseudocoelomate Animals: Nematodes in Depth

1. Chapter 15 Pseudocoelomate Animals Kingdom: Phylum: Class: Order:

2. I. Intro A. General Characteristics of pseudocoelomates a. bilateral, unsegmented, triploblastic, complete gut (tube within a tube), lack circulatory and respiratory systems, dioecious, b. 2 cavities • gut cavity + pseudocoel formed from blastocoel • lack true coelom (peritoneal cavity), not lined w/ peritoneum c. body wall (epidermis)/dermis/muscles surrounding pseudocoel

3. B. Evolutionary Advantages of Pseudocoelom a. ↑ freedom of movement b. space for development (niche)/differentiation of digestive/reproductive/excretory systems c. storage area for wastes d. hydrostatic skeleton

4. C. Structure of a Nematode Identify symmetry?????

5. II. Phylum Nematoda (Nemata): A. Form/Function a. Muscles • longitudinal (no circular), beneath hypodermis • run in 4 bands, marked by 4 hypodermal cords • Hydrostatic pressure • each muscle cells has contractile fibrillarportion (spindle) + noncontractile sarcoplasmic portion (cell body) • sarcoplasmic extends into pseudocoel, stores glycogen • What is glycogen???? • fibrillar is striated w/actin/myosin • See next slide: actin/myosin

7. P. Nematoda (Nemata): Form/Function b. Feeding/digestion • parasitic/predatory • mouth → pharynx → non-muscular intestine → rectum → anus • food sucked into pharynx • muscles contract, lumen expands • intestine is 1 cell thick • food moves posteriorly as new food enters and body moves • defecation occurs via opening anus + allowing pseudocoelomic pressure to expel waste

8. P. Nematoda (Nemata): Form/Function c. How do Nematodes get their energy?? • Anaerobic energy metabolism • Glycolysis??? d. Nervous/sensory system • 2 nerve cords, ventral nerve cords • sensory papillae at head/tail • amphids = pair of sensory organs on head • lead into a deep cuticular pit w/ modified cilia • Dendrites

10. Phylum Nematoda (Nemata): Form/Function d. Reproduction • most dioecious w/ ♂ smaller than ♀ • ♂ has copulatory spicules to hold ♀ vulva open against hydrostatic pressure • internal fertilization • eggs stored in uterus until deposited

11. III. Phylum Nematoda Examples • Common human parasites covered in class • Ascaris (large roundworms) • Pinworms • Hookworm • Porkworm • Filarial worms • Guinea worm

12. 1st Nematode Parasite: Ascaris • Large roundworm of humans (Ascaris lumbricoides) • up to 64% of people in some areas of SE US • +1.2 Billion affected worldwide • infection rates highest in children • ♂ more heavily infected than ♀ • ♀ lays 200,000 eggs/day • eggs pass via host’s feces • embryos develop into infective juveniles in 2 wks • killed by direct sunlight/↑ temp. • resistant to dessication/↓ O2 • eggs remain viable long after fecal matter disappears

13. P. Nematoda: Ascaris continued… • infection via ingestion of eggs (finger/uncooked veggies) • juveniles hatch, burrow through intestinal wall to veins/lymph • carried through ♥ to lungs • break into alveoli and carried up trachea/pharynx • coughed up/swallowed • pass to stomach • mature in intestine after 2 months • feed on intestinal contents • may block/perforate intestines • emerge from anus/throat • enter eustachian tubes/middle ear • Roundworm in dogs/cats • similar life cycle as human roundworm • juveniles migrate to uterus of pregnant dogs • puppies infected

14. 2nd Nematode Parasite: Necator • Hookworms (Necator americanus) • 9–11 mm • hook-like curve on anterior end • dioecious • large plates in mouth cuts into intestinal mucosa • then suck host’s blood • suck more than they digest (anemia) • eggs pass in feces • infective juveniles burrow through skin to blood • travel in blood to lungs • coughed up and swallowed • mature in the intestine • Secrete anticoagulant

15. Life Cycle of Hookworm

16. 3rd Nematode Parasite: Trichina • Trichina worm (Trichinella spiralis) • tiny • + 2.4% of US • trichinosis (potentially lethal) • adults burrow into intestinal mucosa • ♀ directly produce juvenile worms • juveniles penetrate blood vessels/circulate throughout body to all tissues (live 10-20 yrs) • penetrate skeletal muscle • redirecting gene expression of the musculature so it loses its striations • becomes a nurse cell to the parasite • encyst in muscle • excyst when poorly cooked meat containing encysted juveniles is eaten • infect humans/hogs/rats/cats/dogs

17. 4th Nematode Parasite: Enterobius • Pinworms (Enterobius vermicularis) • most common nematode parasite in the US • 30% all children, 16% all adults • causes little disease • + 12 mm • adults live in large intestine/cecum • ♀ migrate to anal region at night/lay eggs (Scotch Tape Method) • itching • scratching contaminates hands and bedclothes • eggs develop/become infective w/i 6 hrs at body temp. • ingested, hatch in duodenum, mature in large intestine • haploid ♂ from unfertilized eggs • diploid ♀ come from fertilized eggs (haplodiploidy)

19. 5th Nematode Parasite: Filarial Worms • Filarial worms • 8 sp. infect humans, 250 million people infected • some live in lymphatic system • cause inflammation/blockage of lymphatics • ♀ release live young (microfilariae) into blood/lymph • mosquitoes ingest microfilariae • worms develop to infective stage • move into mosquito bite wound when it feeds • Elephantiasis caused by repeated exposure • swelling/growth of connective tissue • dog heartworm (Dirofilaria immitis) • most common U.S. filarial worm • transmitted by mosquitoes

22. Incidence in the United States

23. Side note Guinea Worms