1. Examine further the characteristics of
parasitic lifestyles.
2. Appreciate that the ability to move potentially
allows parasites to be more harmful to their hosts. Form an opinion as to
whether the parasites in the phylum nematoda adhere to the rules of being
a parasite.
3. Discuss the advent of the pseudocoel and
contrast this development with the coelom of the previous group.
4. Discuss common trends within the roundworms,
specifically, a complete digestive tract, non-cellular cuticle made of collagen,
ecdysis, parthenogenesis and eutely.
5. Compare the digestive tract, body wall covering,
reproductive pattern, regenerative ability and cell arrangement in flatworms
and roundworms.
6. compare the number of species of free-living
nematodes and parasitic nematodes.
7. Describe the habitat and size of free-living
nematodes, and compare these with parasitic nematodes.
8. Describe the general morphology of nematodes,
and compare the size and form of males and females.
9. Explain what body movements are possible
in nematodes and relate this to the composition and arrangement of structures
in the body wall.
10. Explain a hydrostatic skeleton and how
it works with respect to the cuticle.
11. Compare the excretory systems of parasitic
and free-living nematodes.
12. Describe the reproductive organs and the
unique features of reproduction in general in nematodes.
13. Observe live vinegar eels, describe their
form and activities, and outline their life cycle.
14. Describe the morphology and outline the
lifecycles of the following: Ascaris lumbricoides, Necator americanus, Trichinella
spiralis, Enterobius, and Wuchereria bancrofti.
15. Discuss the impact and diseases caused
world wide by the nematode worms in the previous objective.
16. Describe the size, general appearance and
distribution of rotifers.
17. Describe the food habits and method of
feeding of rotifers, including the function of the corona, mastax and trophi.
18. Define syncytium and describe the unique
features of the cell arrangement in rotifers.
19. Define parthenogenesis and outling the
reproductive pattern of a rotifer species in which there are no males.
20. Outline the reproductive pattern in a rotifer
species in which males occur including the capabilities of amictic and mictic
females.
21. Describe the developments in each of the
following areas: excretion, digestion, nervous function, muscular system
and reproduction.
22. Discuss the evolutionary significance of
the Phylum Nematomorpha. Relate this group to earlier beliefs in spontaneous
generation.
23. Describe the general morphology and body
plan of a horsehair worm and outline a typical life cycle.
Resources: Text: Animal Diversity, Chapter
9
Internet Resources:
http://www.culver.edu/homepages/faculty/mjones/pseudo.htm
http://www.anselm.edu/homepage/chieber/izlabref6b.html
http://dmoz.org/Science/Biology/Zoology/Pseudocoelomates/
http://www.mhhe.com/hickmanad4e
Pseudocoelomates
Ectoderm
gut, endoderm
Pseudocoel
mesoderm
-Tube within a tube
-No peritoneum, therefore, various internal
organs lie free in the cavity;
TUBE-WITHIN-A-TUBE
-permits the mechanical breakdown of food,
digestion, absorption and feces
formation to proceed in a well defined
sequence continually from anterior to posterior
-most important function of pseudocoel is for hydrostatic pressure for "skeleton"
all worms round due to equal outward force generated in all directions
-cavity for circulation, digestion
**Once upon a time: One phyla, Aschelminthes
(asc --> cavity), since then this has
been divided into eight distinct phyla
COMMON TRENDS:
1. psuedocoel ; triploblastic
2. complete digestive tract (except for parasitic forms)
3. non-cellular cuticle made of collagen
-specialized structures (spines, bristles)
4. some forms molt (ecdysis) cuticle
-epidermis secretes new cuticle
-molt necessary because noncellular cuticle can't grow!!
5. Dioecious
6. no ability to regenerate
7. asexual reproduction ---> parthenogenesis
8. Eutely---> constant # of cells and nuclei in adults (mitosis stops)
-constant for whole animal or a given
organ
Ex. nematode C. elegans, # of
somatic cells 959, in pharynx there are 80
9. Cylindrical
10. protonephridia excretory (except
nematodes)
Phylum Nemathelminthes (nematos- thread)
(Nematoda)- round worms
10,000 ---> 500,000 species, most abundant
animal on earth ~5 billion in every
acre of fertile garden soil.
-marine, freshwater, terrestrial (soil)
-parasitic, carnivores, herbivores, omnivores,
saprozoic
-most microscopic but some several meters
-largest pseudocoel phyla
-feed on every conceivable source of organic
matter
-cylindrical
-moncellular, collagenous cuticle, can
be smooth or contain spines, bristles,
warts, redges, all with taxonomic
significance
-cuticle usually molted about 4 times
-no cilia/flagella except in sensory structures
-sperm amoeboid
-tissue/organ grade construction
LOCOMOTION
-longitudinal muscles only, no circular
muscles
-cuticle serves as antagonist rather than another muscle group
-dorso-ventral coiling (thrashing) while laying on its side
-hydrostatic skeleton, internal pressures (*balloon)
DIGESTION/FOOD GETTING
Pharynx only muscular part
-contracts rapidly to suck in food into
lumen (cavity)
-relaxation closes lumen
-muscle contractions pass food posteriorly
-expelled materials shot out by muscle contraction
RESPIRATION (NOT BREATHING)
-much like us (glycolysis, ETS)
-aerobes- complete breakdown of glucose in presence of Oxygen
-anaerobes- glycolysis only in absence of Oxygen
NERVOUS SYSTEM
-ring around pharynx (circumpharangeal)
-2 nerve cords, one dorsal, one ventral
REPRODUCTION- Dioecious
-male smaller
-copulatory organs at posterior
-sperm amoeboid
-Internal fertilization
oviparous- egg layers
ovoviviparous- eggs hatch in mother,
undergo molts
PARASITES -infective stage ususlly larva
-larva develop in intermediate hose (damaging)
-adult in definitive host (vertebrate)
LIFE CYCLES OF COMMON PARASITIC NEMATODES
1. Ascaris lumbricoides (Round
worm)
-most common human parasite
-females capable of ~200,000 eggs/day
a. eggs enter body through contaminated
water, green veggies,
unsanitary conditions (eggs
in feces)
b. mouth to small intestine where
eggs hatch.
c. young penetrate wall of intestine into blood stream
d. travel to heart ---> lung capillaries (alveoli)
e. from capillaries up respiratory
tract to pharynx (esophagus) where they are
swallowed and reach intestine
to grow
2. Hookworm- Necator americanus
a. similar to Ascaris
-adult in sm. intestine ---> eggs (non-infective) pass in feces
-larva feed on organic material/bacteria
-molt twice, then infective
-larva penetrate skin upon contact (ground itch)
-enters blood ---> lung ----> intestine
b. once in intestine cutting mouth
parts attach to wall
c. suck blood (more than necessary);
anticoaggulant
3. Trichinella spiralis - trichinosis
(potentially lethal in large #)
a. acquired by injesting poorly cooked
pork
b. most damage done by migrating larva from intestine to muscle
c. juvenile encyst in muscle and become calcified
d. common life cycle
-adult in small intestine of
rat/mouse
-larva encyst in muscle
-pig eats infected rat/mouse; worms mature and produce new larva in flesh of pig
-poorly cooked pork, smoked sausage eaten by man
-larva become adult ---> eggs ---> encyst in human muscle
**degeneration of muscle, inflamations
4. Pinworms- most common nematode parasite
in U.S.. Enterobius fortunately not
very harmful
-live in large intestine
-females become distended w/ eggs and
lose grip on intestine, move w/ prevailing
currents to anus
-crawl and lay eggs about anal and vaginal
openings, creates itch
-scratching gets them under fingernails, nails to mouth, etc
5. Filarial worms- Wuchereria bancrofti
-major diseases, So. Pacific, Elephantiasis
1. worms live in lymphatic system
2. adults in lymph nodes ---> larva into blood
3. mosquito bites man taking up larva
4. larva matures in mosquito
5. larva reenters human w/ mosquito
bite
Elephantiasis- chronic infections,
excessive growth of connective tissues of infected parts
-plug nodes cause swelling
PHYLUM NEMATOMORPHA- horsehair worms
-formerly thought to arise spontaneously
from the hairs of horses tail in drinking troughs
or other stock watering places
-adults free living but juveniles parasitic in arthropods
-larva must quickly enter host quickly after hatching
-worm leaves host only when near water
PHYLUM ROTIFERA- wheel bearing ciliated crown (corona)
-small
-mostly freshwater, few marine
-epizoic (live on surface of other animals)
-planktonic forms ciliated for locomotion
-Benthic ciliated for food gathering
-predator, herbivore, detritivore
BODY PLAN
-pseudocoel (big surprise!!)
-pseudosegmentation, telescoping, no
molt, cuticle must stretch for growth
(Eutely ~ 1000 cells; organs eutelic
as well)
-head contains corona, may be retracted
or not, cilia of corona, create currents;
food in, locomotion
-mouth opens into mastax (muscular pharynx)
appears as a beating heart, mastax
unique to rotifers
-mastax has trophi, jaws used for grasping
and chewing used for species classification
-trunk, pseudocoel ---> stomach, intestine
-foot, not always present, means of anchoring
EXCRETORY SYSTEM
-Protonephridia (2), tubules w/flame cells
along length of body. osmoregulatory in nature
-drain into cloaca that leads to anus
-cloaca common cavity into which digestive
excretory and reproductive systems connect
DIGESTIVE SYSTEM- complete mouth ---> anus
Stomach shows extracellular digestion
mastax ---> esophagus ---> ciliated
stomach ---> salivary and digestive glands secrete
digestive enzymes into pharynx and stomach
NERVOUS SYSTEM
bilobed brain (ganglionic) located anterior,
nerve cords, sensory bristles, "eyes", ciliated
sensory pits
MUSCLES- longitudinal and circular
1. move foot, toe
2. control corona
3. extend body (telescoping)
REPRODUCTION
-all dioecious w/ internal fertilization
(adaptation to freeliving mode of life)
-males few and far between, usually degenerate
(no digestive), testes comprise most of
body
LADIES PLEASE REFRAIN FROM MAKING WILD
COMPARISONS!!!
-reproduction sexual although several types of parthenogenesis occur
Class Monogononta (2 egg types)
Amictic eggs (thin shelled, summer
eggs)
-produced by mitosis, therefore,
diploid eggs (2N)
-develop directly into amictic females
Mictic eggs (thin shelled, Haploid)
-if eggs not fertilized --->
devel partheno into male
-if fertilized ---> mictic egg secretes a thick, heavy shell and becomes dormant
-hatch with melting snows and spring rains into amictic females (2N)
-most females lay either amictic or mictic eggs, but not both