Week 8
I. Phylum Platyhelminthes
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flatworms
no segmentation
bilateral symmetry
triploblastic (3 germ layers) – development of a mesoderm ( gives rises to
excretory and reproductive systems  compare to sponges and cnidarians
tissue-organ level of organization  compare to sponges and cnidarians
aceolomates – body cavity filled with parenchyma= loose mesodermal cells
Digestive System
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incomplete digestive tract
mouth, pharynx and intestine
mouth on the ventral side of the body
no anus (regurgitate food)
Respiratory System
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oxygen taken in and carbon dioxide released through diffusion
Nervous System
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cephalization of anterior end with clumps of nerves called ganglia (brain)
2 nerve cords run from the brain to tail
ladder type of nervous system (connections run horizontally between the nerve
cords)
Excretory System
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flame cells control excretion and osmoregulation
Reproductive System
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monoecious ( have both testes and sperm)
asexual reproduction – detachment of the tail into 2 halves = transverse fission
sexual reproduction
Classes:
(1) Turbellaria eg Dugesia
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planarians
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free living
ciliated epidermis for movement
have ocelli = eyespots for the detection of light which they move away
from
have auricles which are tactile and olfactory in function
regeneration possible
http://dragon.seowon.ac.kr/~bioedu/bio/ohp/t-162.jpg
http://cas.bellarmine.edu/tietjen/images/platyhelminthes.htm
http://cas.bellarmine.edu/tietjen/images/platyhelminthes.htm
(2) Monogena eg Polystoma
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flukes
parasitic
common on the skin or gills of fish
no asexual reproduction
(3) Trematoda eg Clonorchis, Schistosoma
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flukes
parasitic (endoparasites – live inside the host and ectoparasites – live
on the surface of the host)
tissue and blood flukes
Chlonorchis Life Cycle
www.dpd.cdc.gov/.../ body_Clonorchiasis_page1.htm
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several hosts involved in life cycle
eggs are released from the host in the feces
eggs hatch into free-swimming forms (miracidia) when they reach water
miracidia enter a snail or other mollusk (intermediate host) and become
sporocysts
cells of the sporocysts undergo mitosis forming rediae
rediae give rise to free-swimming cercariae that escape from the mollusk into
water
cercariae penetrate another host, usually an arthropod using enzymes
the penetrated cercariae encyst forming metacercariae
when the arthropod is eaten by the definitive host (human), the metacercariae
excyst and develop into eggs
repetition of the cycle
Schistosoma Life Cycle
www.drnatura.com/ parasites.html
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similar life cycle to Chlonoris
eggs are released in water either from the urine or feces depending on the strain
eggs hatch hatch into free-swimming forms (miracidia)
miracidia enters a snail and become sporocysts
cells of the sporocysts undergo mitosis producing cercariae
cercariae are released into water from the snail
penetration of the skin of the human host by the cercaria which secretes enzymes
that break down the skin's proteins enabling penetration of the cercaria through
the skin
transformation of the cercariae into a migrating schistosumula stage
schistosomula travels through the blood to the lungs where it undergoes further
developmental changes before it migrates to the liver
the worms pair and then move either to the mesenteric or rectal veins
onece mature enough (~ 6-8 weeks after invasion) they produce eggs
the eggs pass through the walls of the blood vessels, and through the intestinal
wall and are released from the body in the faeces (S japonicum and S. mansoni)
or the eggs pass through the bladder wall and into the urine (S. haematobium)
Schistosomiasis (Bilharzia)
o eggs trapped in the body mature and begin secreting antigens
o these antigens elicit a violent immune response
(4) Cestoda eg Taenia, Diphyllobrothium
- tapeworms
- parasitic
- live in the digestive tract of vertebrates – adult form
- no digestive tract or mouth
- scolex (with hooks) used for attachment to the intestine of the
host
- neck divides to form new proglottids
- proglottids contain the reproductive structures
- flame cells (protonephridia) used for excretion
- gravid proglottids (mature) leave the host via the feces
Taenia Life Cycle
http://www.dpd.cdc.gov/dpdx/HTML/Taeniasis.asp?body=Frames/S-Z/Taeniasis/body_Taeniasis_page1.htm
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pigs may contain cysticerci embedded in their muscles by eating contaminated
vegetation
oncospheres hatch in the pig’s intestine and then migrate to the muscles where
they become cysticerci
cysticerci are ingested by humans eating undercooked meat (pork/beef)
cysticerci consist of a capsule containing a scolex.
upon ingestion of the worm, the gastric juice in the stomach dissolves the wall of
the capsule and the scolex turns inside out and attaches by suckers and hooks to
the wall of the intestine
proglottids are then produced from the scolex and remain attached as they mature
developing both male and female sex organs in each
gravid (mature) proglottids break off and are passed out in the feces, each
containing the fertilized eggs
life cycle repeats itself
http://cas.bellarmine.edu/tietjen/images/platyhelminthes.htm
II. Phylum Nematoda (nematode = thread)
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roundworms
psuedoceolumates
no cilia
bilateral symmetry
triplobalstic
tissue-organ level of organization
long, narrow cylindrical body tapered at both ends
virtually no head
epidermis secretes a thick, tough yet flexible cuticle
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cuticle protects the worm from drying out or being crushed
cuticle is shed as the organism matures (~ 4 times before reaching the adult stage)
= molting
longitudinal muscles allow to bend from side to side, appears to thrash from side
to side (no circular muscles)
parasitic or free-living
Digestive System
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complete digestive tract
mouth  anus
Respiratory System
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oxygen taken in and carbon dioxide released through diffusion
Nervous System
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ring of nerve tissue around the pharynx gives rise to 2 nerves (dorsal and ventral)
that run along the length of the body
Excretory System
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no flame cells
Reproductive System
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most are dioecious
males are smaller than females
sexual reproduction = copulation
male attaches to the female by copulatory spines and injects the sperm into the
genital pore
sperm lack flagella but move by pseudopodia
Ascarias Life Cycle
http://www.infovek.sk/predmety/biologia/metodicke/hlistovce/obrazky/AscariasisLifeCycle.gif
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adult worms live in the small intestine
eggs are passed with the feces
eggs become infective after 18 days to several weeks depending on the
environmental conditions (moist, warm, shaded soil).
when eggs are swallowed, larvae hatch
larvae invade the intestinal mucosa
from the intestine they are and are carried via the portal circulation, then systemic
circulation to the lungs
larvae mature in the lungs (10-14 days)
larvae penetrate the alveoli
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from the alveoli they move up the bronchial tree into the throat where they are
swallowed and return to the small intestine and mature into adults
III Phylum Annelida
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segmented worms
earthworms, leeches and polychaetes
triploblastic
ceolomates – body wall is divided into compartments by septa
circular and longitudinal muscles
cuticle secreted by the epithelial cells
all have setae (except leeches) – hair-like structures made of chitin
setae can be located on parapodia (appendages)
Segmentation = metamerism (characteristic feature of annelids)
- each segment contains elements of the circulatory, nervous, and excretory tracts.
- increases the efficiency of body movement by allowing the effect of muscle
contraction to be extremely localized
Digestive System
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complete
mouth  anus
Respiratory System
- gas exchange through the skin or specialized gills or modified parapodia
Circulatory System
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closed
Nervous System
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a pair of cephalic ganglia attached to double nerve cords that run the length of the
animal along the ventral body wall
there are ganglia and branches in each segment.
tactile organs, chemoreceptors, balance receptors, and photoreceptors
some have well developed eyes, including lenses.
Reproductive System
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monoecious or dioecious
asexual reproduction = fission (posterior part of the body breaks off and forms a
new individual)
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sexual reproduction = copulation
Two worms attracted by each other's secretions lay together with their heads
pointing opposite directions and fluid is transferred from the male pore to the
female worm.
Classes:
(1) Polycheata
http://www.mytobago.info/photos/diving/hazards/bristle-worm.jpg
- bristleworms
- marine
- have parapodia (vascularized) used for movement and gas exchange
- well developed heads
(2) Oligocheata
http://www.bu.edu/lernet/GK12/eric/earthworm.jpg
- earthworms
- freshwater and terrestrial
- hermaphroditic
- no appendages/parapodia
- few setae
- spacious coelom used as a hydrostatic skeleton
- external fertilization
- no trocophore larvae stage
(3) Hirudenia
http://en.wikipedia.org/wiki/Leech
- leeches
- freshwater, terrestrial and marine
- all are carnivorous
- some are predatory - feed on blood
- hermaphroditic
- no appendages/parapodia
- ventral sucker formed from the last 6 segments of the body  used to
connect to a host for feeding
- release an anesthetic to make host unaware of their presence
- secrete an anti-clotting enzyme into the blood of the host