Phylum Platyhelminthes the flatworms

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Phylum Platyhelminthes - the flatworms life in
two dimensions
bilaterally symmetrical, 3 germ layers, most have
gut, but not complete (no anus), marine,
terrestrial fresh water no body cavity (coelom
or pseudocoel) hermaphroditic, sperm with two
tails some direct some indirect developers,
spiral cleavage, many (esp. parasites) have
multiple life stages respiration by diffusion
multiciliated epidermal cells very limited
fossil record some supposed trace fossils, some
recent classically, four
classes (probably not true taxonomic - i.e.
monophyletic - groups) ? class Trematoda -
flukes, the largest group of flatworms all are
parasitic ? class Cestoda - tapeworms, all all
are internal parasites, no gut ? class
Turbellaria - most are non-parasitic, includes
? Class Monogenea - all ectoparasites planarian
s and the polyclads
? ....and
new evidence suggests that the Acoela may belong
in their own phylum
fossilized eggs
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flatworm anatomy (a cestode)
JA Pechenik (2000) Biology of the
Invertebrates Figure 8.12
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turbellarian anatomy
Dugesia (triclad, fresh water) eyes
protonephridia (flame cell)
Dugesia nervous system
brain, detail
http//cas.bellarmine.edu/tietjen/images/platyhelm
inthes.htm
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the trematodes - flukes
Deformed Pacific Treefrog, Hyla regilla, from
Oregon, with supernumerary hind limbs
(cyst-induced) (photograph by S. K. Sessions).
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http//www.hartwick.edu/biology/ def_frogs/Introdu
ction/Riblifecycle.html
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another nasty fluke...
http//www.biosci.ohio-state.edu/ parasite/lifecy
cles/ schistosoma_lifecycle.html
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life cycle of the hydatid tapeworm, Echinococcus
granulosus
http//www.vetpath.usyd.edu.au/parasitology/tape/c
estodes.htm
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human tapeworm Taenia spp.
"holdfast" with 4 suckers
http//www.biosci.ohio-state.edu/parasite/taenia.
html