Transcript unit 3b free-living roundwormsx

Journal #1
What is one thing you know about
roundworms?
What is one thing you want to learn about
roundworms?
Phylum Nematoda
I.
General Information:
1.
Round, unsegmented bodies tapered at each end
2.
Pseudocoelom- body cavity filled w/fluid that distributes
oxygen & nutrients so don’t have circulatory system
3.
Tube-within-a-tube body plan
4.
2 body openings- mouth & anus
5.
Size- microscopic to about 1 meter
6.
Bilateral symmetry
7.
Triploblastic
8.
Most are free living
some are parasitic
II. Body
a.
Cuticle-
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Thin, tough outer skin may have
spines or scales for protection.
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Not easily digested by host
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Most molt about 4x during life
b.
Longitudinal muscle-
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Produces thrashing motion
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Creates S- or C-shaped curves
III.
Digestion/Feeding
a.
Parasitic, free living, saprobes
(decomposers)
b.
Mouth- buccal cavity
•
May have hooks or suckers for
attaching (parasite)
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Sensory organs (“lips”) may be present
c.
Pharynx- muscular organ that
rhythmically pumps food thru digestive
tract
d.
Intestine- long tubular organ where
digestion/absorption occur
e.
Rectum/Anus- end of digestive tract
where wastes are excreted.
IV. Nervous System
a.
Dorsal & Ventral Nerve Cord- run
along upper & lower surface of
body sending nerve impulses to
anterior end.
b.
Nerve ring- simple brain picks up
stimuli from nerve cords.
c.
amphids – anterior (towards the
head) depressions used for sensing
chemicals in the water
d.
phasmids – posterior (towards the
tail) depressions used for sensing
chemicals in the water
V. Respiration
a. All roundworms
breathe by diffusion of
oxygen into moist skin
and carbon dioxide out
of moist skin.
VI. Excretory System
a. Excretory ducts collect
liquid waste
b. Excretory pores
excrete collected
liquid waste thru skin
VII. Reproductive system
a.
Dioecious
b.
Males are usually smaller than
females
c.
Most lay eggs that hatch into larvaoviparous
d.
Some give birth to live larva- viviparous
e.
Some create eggs which they retain &
hatch inside body- ovoviviparous
f.
Some males may have bursa- flap of
skin used to hold female while
transfering sperm
•
May also have copulatory spikes or
spicules which are penis-like
g. Typical Nematode Life Cycle
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Egg
L1- 1st larval stage
L2- 2nd larval stage
L3- 3rd larval stage
L4- 4th larval stage
Adult
Molt in between each larval stage
to get bigger
• Dauer- after 1st molt larvae may enter
this hibernation stage if overpopulation
pheromone is present, temperature is
too high, or no food present.
Parasitic nematodes have
different life cycles
VIII. Economic/Environmental
Importance
a.
Free-living soil nematodes
& saprobes- important as
recyclers of necessary
nutrients back to soil.
•
1 m2 of mud = 4 million
nematodes!
b. Parasitic nematodes- Cause
disease
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Plants
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Vertebrates
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Humans
1. Nematodes are
a. Monoecious
b. Dioecious
2. Nematodes are the first animals we have study to have
a.
Nervous system
b. Mouth and anus
c. Excretory system
3. The structure that helps prevent digestion of parasitic
nematodes is the
a. Cuticle
b. Hook
c. sucker
DAILY
Males are larger than females
QUIZ
Females are larger than males
#1
Neither A or B because they are hermaphrodites
4. Which is true about nematodes
a.
b.
c.
5. Which is not a characteristic of nematodes?
a. Bilateral symmetry
b. Triploblastic
c. Pseudocoelom
d. Segmented