Week 9: Lower Invertebrates
Can Be Classified Based On These 3 Different Categories:
1. The presence or absence of
.
2. Body Symmetry
3. Presence or absence of
h
Invertebrates
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Belong to
m
a
Multicellular Organisms
s
Body structures vary
They occupy almost every habitat and account for 95% of all known animal species.
Phylum Porifera:
The Sponges
 Also known as
s
 Lack true tissues and organs, and are mostly marine

s: Remain in one place throughout life.
 Spongy skeleton made by
s which are secreted by amoeboid cells
 Undergo filter-feeding by creating a water current with the use of flagella on their
s
 Simplest spongy form contain
m
SPONGEY REPRODUCTION
 Asexual
o Regeneration
o Budding
o Gemmules
 Sexual
o Dioecious
o Monoecious
Eumatazoans
 All have
tissues
 Have two different types of Symmetry:
 Bilateral
 Radial
Radial Eumatazoans
 Have several planes of symmetry down a central axis .
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No ability to differentiate between front, back, left, and right.
Contain
l and
l surfaces.
Some examples include: Jellyfish, Hydra, Coral, Sea Anemones
Phylum Cnidaria
o Class Hydrozoa
o Class Scyphozoa
o Class Anthozoa
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Phylum Ctenaphora
Phylum Cnidaria
 Jellyfish, Hydra, Sea Anemones
 Have true tissues (
a)

l Symmetry

: 2 tissue layers
o Epidermis (outer layer)
o Gastrodermis (inner layer)
 Incomplete digestive tract, primitive organ development
 No anus – waste passes through the mouth!

s - specialized cells that contain stinging
structures called
s
THREE CLASSES OF PHYLUM CNIDARIA
 Class Hydrozoa
o alternate between medusa and
P form
o Polyp form is dominant
o examples: Portuguese man-o’war, hydra,
fire coral
 Class Scyphozoa
o alternate between
A and polyp form
o Medusa form is dominant
o examples: jellyfish, box-jellyfish, sea wasps
o Some “Box-Jellyfish” have poisonous stingers
 Class Anthozoa
o
P form only!
o examples: most corals, sea fans, sea
anemones
PHYLUM CTENOPHORA
”
 Possess 8 comb rows of fused cilia
 Largest organism to use
!
 Usually have a pair of
e tentacles
 Resemble the medusa stage of cnidarians
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C : 2 tissue layers
 Exhibit bioluminescence
 No nematocysts (usually)
 Have cells called
s for adhesion to capture prey
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c - move with the ocean currents
Bilateral Eumatazoans
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Animals that possess bilateral symmetry can be cut in half along the central axis.
has evolved, resulting in
the use of their head for
n.
: Have three germ layers.
Phylum Platyhelminthes
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Also known as “Flatworms”
c: 3 germ layers
Ectoderm:
r layer
Mesoderm:
e layer
Endoderm:
r layer
: no body cavity
Gas exchange occurs across body surface
Hermaphrodites : male and female parts
Phylum Nemertea
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Commonly called “Ribbon” worms
Possess a proboscis for feeding/capturing prey
Phylum Rotifera
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Microscopic organisms
e body cavity
Complete digestive tract with mouth and anus
Many reproduce via
s(asexual reproduction where embryo
development occurs without fertilization)
Phylum Nematoda
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e body cavity
Free-living and parasitic species
Extremely abundant
Bodies are
d
Only have
l muscles
Whips back and forth
Phylum Mollusca
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s: Coelom or body cavity completely lined with
s (mouth forms first – before anus)
Aquatic and terrestrial forms
o Respiration mostly through gills
o Terrestrials use vascularization of the mantle cavity as a lung
Calcium carbonate shells
Body parts:
Mantle
Head/foot
Visceral mass (
)
Shell (usually)
Radula for
g
m