The Big Picture
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DEFINING CHARACTERISTCS OF ANIMALS
1. Heterotrophs: ingest their food
2. Multicellular:
3. Eukaryotic: animal cells with a nucleus and
organelles – large diversity of cell specialization
4. No cell walls
TWO MAIN DIVISIONS:
Invertebrate: all other phyla without internal
skeletons
Vertebrate: Phylum Chordate – internal skeleton
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Cellular – Porifera
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Tissues – Cnidaria
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Organs- all others
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Cephalization is considered an evolutionary trend,
whereby nervous tissue, over many generations,
becomes concentrated toward one end of an
organism. This process eventually produces a head
region with sensory organs.
Cephalization is intrinsically connected with a change in
symmetry. It accompanied the move to bilateral symmetry
made in flatworms, with ocelli and pinnae placed in the
head region.
In addition to a concentration of sense organs, all animals
from annelids on also place the mouth in the head region.
This process is also tied to the development of an anterior
brain in the chordates from the notochord.
A notable exception to the trend of cephalization throughout
evolutionary advancement is phylum Echinodermata, which have
Pentamerous Radial Symmetry – Echinoderm Adults only
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None – Porifera
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Radial – Cnidaria
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Bilateral – All others
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Pentamerous Radial Symmetry – Echinoderm Adults
only
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•
•
•
Endoderm - digestion and respiration
structures
Mesoderm - muscles, bones, blood, and
reproductive organs
Ectoderm - skin, brain, and nervous system
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None – Porifera
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Diploblastic – Cnidaria
 endoderm & Ectoderm with mesoglea between
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Triploblastic – All others
 Endoderm, Mesoderm, Ectoderm
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Diploblastic Acoelomate – Cnidaria
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Triploblastic Acoelomates – Platyhelminthes
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Pseudocelomate – Nematoda
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Coelomates – Annedlida and everything above
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Cnidaria
No cavity between body
wall & digestive tract
Digestive
Cavity
Digestive
Lining
Solid
Tissue
Body Wall
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Nematoda
Body cavity partially lined
with mesoderm
Digestive Cavity
Digestive Tract
Pseudocoelom
Partial Lining
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Annelida
Body cavity completely
lined with mesoderm
Digestive Cavity
Digestive Tract
Coelom
Complete Lining
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Bilateral animals can be divided into two main
groups based on embryological development
Protostomes
Body cavity forms within a space between the body
wall and the digestive cavity
› Blastopore becomes mouth
› e.g. nematodes, arthropods, flatworms, annelids,
mollusks
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Deuterostomes
Body cavity forms as an outgrowth of the digestive
cavity
› Blastopore becomes anus
› e.g. echinoderms, chordates
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Protostome
Deuterostome
•Coelom forms from
the solid masses in the
embryo
•blastopore becomes
the mouth
• Coelom forms from a
portion of the digestive
tube
•blastopore becomes the
anus
• spiral / determinate
cleavage
• radial / indeterminate
cleavage
• mosaic development
• regulative development
(Annelida, Arthropoda,
Mollusca,)
(Echinodermata, Chordata)
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5. Reproduction: Asexual and sexual
 A. Direct development: “Babies” (offspring)
look like adults (they get bigger as they get
older, but don’t change)
 B. Indirect development: Metamorphosis
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Ex) Tadpole to frog
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Herbivores: Eats plants
Carnivores : Eats animals
Omnivores : Eats plants and animals
Parasites : Lives off of a host
Filter Feeders : Strains floating plants and
animals from surrounding water
Detrivores : Feeds on decaying plants and
animals (detrius)
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Feeding – see above
Respiration – skin or full system
Internal Transport – closed or open circulation
Excretion – waste removal
Response – nerve cells – brain- specialized
organs
Movement – exo or endoskeleton, muscles
Reproduction – sexual or asexual
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Simplest Animal - Commonly referred to as
Sponges
Adults are sessile- can’t move on their own
Lack true tissues and organs, most are
unspecialized – Cell Level of Organization
Incomplete digestive system
No Symmetry
Ancient & mostly marine
Close to 5,000 species divided into 3 classes:
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Outer layer protects the interior and has many holes
through which water can enter the sponge
Inner layer are lined with collar cells, which have
flagella
Amoebocytes wander through the jelly-like material
and pick up food from the collar cells for digestions,
transport oxygen, dispose of waste and can change into
other cells for support
Have special chemical defenses to protect from
predators, disease organisms, humans use these
chemicals
Related closely to protists and are the earliest animals.
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Porocytes: water goes thru them into central
cavity
Collar Cells: move water current thru the pores
via flagella
Osculum: opening that water exits cavity thru
Spicules: form skeleton
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Some sponges have skeletons made by both CaCO3
and SiO2.
Amebocytes: build the spicules
Note: water flow = nutrients in and waste out
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Filter Feeders!
Sponges are characterized by the possession of a
feeding system unique among animals. Poriferans
don't have mouths; instead, they have tiny pores in
their outer walls through which water is drawn. Cells
in the sponge walls filter goodies from the water as
the water is pumped through the body and out other
larger openings. The flow of water through the
sponge is unidirectional, driven by the beating of
flagella which line the surface of chambers connected
by a series of canals. Sponge cells perform a variety
of bodily functions and appear to be more
independent of each other than are the cells of other
animals.
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Sexual: - sperm are release into the water thru
pores amebocytes carry to eggs  zygote 
larvae swim & settle  new sponge
Asexual:
Gemmules: sphere of amebocytes & spicules
that can survive freezing or drying
Budding: part falls off  new sponge
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›
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Tissue Level of Organization - Cells organized into
distinct tissues
Rudimentary nerve network and contractile tissue
No true organs
Incomplete Digestive System - One digestive opening
Reproduce sexually and asexually
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Radial symmetry, most do not have a head and are
sessile
Tentacles with stinging cells called cnidocytes
Has poisonous barbs called nematocysts, that fire when
touched, once prey has been captured, the tentacles
move it to the gastovascular cavity
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Polyp-cylindrical
body with tentacles
radiating from one
end, sessile
Medusa- umbrella
shaped form with
fringed tentacles on
the lower edge, move
freely
Some cnidarians exist
in both forms and
some one or the other
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Hydrozoa- sessile polyps & medusa stages –
often found in colonies – hydra, man-of-war
Scyphozoa- mostly medusa, v short polyp –
some very toxic - jellyfish
Anthozoa- only polyp - sea anemones & most
corals
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