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 fibrillar portion (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 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
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