Patterns of Organization
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Just like body symmetry, body patterns are
another form of organization used to classify
animals.
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Unicellular
Diploblastic
Triploblastic
Diploblastic Organization
Derived from 2 embryological layers:
Ectoderm: gives rise to
the epidermis (outer
layer of body wall)
Endoderm: gives rise
to the gastrodermis
(lining inside the gut)
Figure 7.10
Diploblastic Organization
Functionally
interdependent tissue
layers.
Gastrodermis-digestive
and muscular cells
Epidermis-epithelial
and muscular cells
Ex: Hydra & jellyfish
Figure 7.10
Triploblastic Organization
Derived from 3 embryological layers
Mesoderm: gives rise to supportive, contractile, and blood cells
Most have organ-system level organization (excretory, nervous,
digestive, reproductive, circulatory, etc.)
Triploblastic Organization
Body cavity is a fluid-filled space in which the internal organs can be
suspended and separated from the body wall.
3 subgroups………….
Coelomate
(SEE lom ate)
Body cavity completely
surrounded by
mesoderm
• Organs suspended in
the body cavity
Pseudocoelomate
Body cavity not entirely
lined by mesoderm
No suspended organs,
muscular or connective
tissue
Acoelomate
Without a coelom
Mesoderm forms a solid
mass between ectoderm
and endoderm called
parenchyma (no particular
function)
The Triploblastic,
Acoelomate Body Plan
Chapter 10
Triploblastic, Acoelomate Body Plan
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1st animals to exhibit bilateral symmetry and
a body organization more complex than that
of the sponges.
Triploblastic (3 primary germ layers)
Acoelomate (without a coelom)
Phyla
Platyhelminthes
 Nemertea
 Gastrotricha
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Platyhelminthes
Greek platys=flat and helmins=worms
“Flat Worms”
Phylum Platyhelminthes
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34,000 species
Range from 1 mm or less to 25 m
Mostly worm like creatures that are flattened
body design
Tapeworms, Flatworms, Flukes and
Planarian.
Characteristics
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Bilateral symmetry
Usually flattened &
unsegmented
Degree of
cephalization
Sac-like digestive
system; absorb food
Ladder nervous
system
Monoecious: complex
reproductive systems
Digestion
Varies from simple
unbranched
chamber to a highly
branched system of
tubes
Class Turbellaria
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Freshwater & marine free living bottom
dwellers
Crawl on rocks, sand and vegetation
Predators and scavengers
Colorization mostly black, brown & gray
(marine groups brightly colored)
Blind gut (one-way gut); mouth but no anus
Photophobic; have eyespots that detect light
Outer Body Covering
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Covered by a ciliated epidermis
Rhabdites: rod-shaped cells that swell to
form a protective mucous sheath around the
animal, possibly in response to attempted
predation or desiccation
Adhesion glands: produce a chemical that
attaches part of the animal to a substrate
Releaser glands: secrete a chemical that
dissolves the attachment
Locomotion
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Bottom dwellers glide over substrate using
cilia and muscular contractions help twist &
turn
Lay down a sheath of mucous that aides in
adhesion and helps the cilia gain traction
Nutrition
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Most are carnivores and feed on
small, live invertebrates or
scavenge on larger dead animals
Chemoreceptors (auricles):
Sensory cells on their head help
detect food
Feeding is via a pharynx:
muscular opening to the one-way
gut that is located mid-body
The pharynx will pin down the prey
while enzymes secreted from the
mouth soften the tissue. The
mouth sucks in the food and
digestion is completed inside the
cells.
Figure 10.5
Class Turbellaria
Internally, no body cavity: organs are held in parenchyma,
non-contractile muscle cells that take up space
Reproduction & Environment
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Use crossfertilization
Monoecious:
Hermaphroditic
Can reproduce
asexually by
transverse fission
Produce zooids
Figure 10.8