Lecture
Outline
1. 
2. 
3. 
4. 
5. 
6. 
7. 
What
is
an
animal?
Origins
Morphological
trends
Gastrula=on
Body
cavity:
the
coelom
Protostomes
&
Deuterostomes
General
classifica=on
of
animals
What
is
an
animal?
•  Mul=cellular
heterotrophs:
feed
by
inges&on.
•  How
does
this
differ
from
plants,
fungi,
pro=sts?
What
is
an
animal?
•  Carbohydrates
stored
as
glycogen
•  Polysaccharide
of
glucose
•  (no,
you
do
not
need
to
know
this
structure)
What
is
an
animal?
•  No
cell
walls
•  Cells
supported
by
structural
proteins:
collagen
–  Extracellular
matrix,
supports
=ssues,
gives
cells
structure
from
outside
–  Triple‐helix
structural
protein
What
is
an
animal?
•  Nerve
and
muscle
=ssue
•  Impulse
&
movement
What
is
an
animal?
•  Generally,
most
have
sexual
reproduc=on
from
anisogamous
or
heterogamous
gametes.
What
is
an
animal?
• 
• 
• 
• 
• 
• 
Egg
+
Sperm

Zygote
cleavage

Blastula

Gastrula

Larva
or
juvenile

Adult
•  This
development
regulated
by
Hox
genes
Animal
Diversity
• 
• 
The
vast
majority
of
animal
species
are
marine
Only
truly
terrestrial*
animals
come
from
5
phyla
– 
– 
– 
– 
– 
• 
Mollusca
Annelida
Onychophora
Arthropoda
Chordata
*Does
not
include
internal
parasites
nor
taxa
needing
constant
external
moisture
Animal
Origins
•  Monophyle&c
•  Sister
taxon
Choanoflagellates
(pro=st
Protozoa)
•  Colonial,
flagellated
pro=st
ancestor
Animal
Origins
•  Gastrula‐like
infolding
into
two
layers
•  Increased
specializa=on
of
cells
and
=ssues
beginning
with
soma&c
vs
reproduc&ve
Animal
Origins
•  Molecular
evidence:
–  Suggests
divergence
from
fungi
~1
bya
–  Common
ancestor
of
animals
675‐875
mya
Animal
Origins
•  Fossil
evidence:
– Possible
trace
fossils
~900
mya
– Ediacaran
fauna
610‐550
mya
• Animals???
– Definite
animal
fossils
(about
1/2
of
phyla)
appear
during
Cambrian
Explosion.
Animal
Origins
The
Cambrian
Explosion
•  Why
so
sudden?
1.  Predator‐Prey
interac=ons
and
coevolu=onary
arms
races.
2.  Increase
in
atmospheric
oxygen
allows
for
larger
animals
with
higher
metabolic
rates.
3.  Key
innova&on
of
Hox
genes
allows
rapid
diversifica=on
of
developmental
pathways.
Morphological
Trends
Symmetry
•  Radial
vs
bilateral
•  Radial
–  Top
and
bohom
only‐‐
no
lei
or
right
–  Likely
ancestral
trait:
Cnidarians,
Ctenophores
Morphological
Trends
Symmetry
•  Radial
vs
bilateral
•  Radial
–  Top
and
bohom
only‐‐
no
lei
or
right
–  Likely
ancestral
trait:
Cnidarians,
Ctenophores
Morphological
Trends
Symmetry
•  Radial
vs
bilateral
•  Bilateral
–  Top‐bohom,
forward‐
backward,
lei‐right
–  Allowed
cephaliza&on,
more
ac=ve
lifestyle.
Morphological
Trends
Tissues
•  Porifera
or
Parazoa
(sponges)
lack
true
=ssues
(this
is
a
unique
development)
Gastrula=on
•  Germ
layers
are
formed
by
the
process
of
gastrula&on
•  One
end
of
blastula
folds
inward,
eventually
produces
layers
of
embryonic
=ssue
Gastrula=on
•  Blastula
is
a
mul=‐
cellular
embryonic
stage
that
is
typically
a
hollow
ball
of
cells
that
surrounds
a
cavity
called
a
blastocoel
Gastrula=on
•  The
invagina=on
or
gastrula=on
results
in
the
gastrula
stage
•  The
pouch
formed
is
called
the
archenteron
and
the
opening
to
the
outside
is
called
the
blastopore
Gastrula=on
•  Animals
with
only
ectoderm
and
endoderm
have
only
gastrula=on
as
germ
layer
forma=on
•  Cnidaria
(jellies)
and
Ctenophora
(comb
jellies)
•  Diploblas&c
Gastrula=on
•  All
bilateral
animals
have
a
third
germ
layer,
the
mesoderm
•  Forms
muscles
and
most
organs
between
diges=ve
tract
and
the
outer
covering.
•  Triploblas&c
Body
Cavity:
The
Coelom
•  Most
triploblas=c
animals
have
a
body
cavity
–  Fluid‐
or
air‐filled
space
separa=ng
the
diges=ve
tract
from
the
outer
body
wall.
•  This
is
the
coelom
Body
Cavity:
The
Coelom
•  The
coelom
forms
from
=ssue
derived
from
mesoderm
•  COELOMATES:
–  Mesoderm
connects
dorsally
and
ventrally
and
provides
a
complete
lining
of
the
coelom
Body
Cavity:
The
Coelom
•  The
coelom
forms
from
=ssue
derived
from
mesoderm
•  PSEUDO‐
COELOMATES:
–  Coelom
is
lined
with
mesoderm
(outside)
and
endoderm
(inside)
Body
Cavity:
The
Coelom
•  The
coelom
forms
from
=ssue
derived
from
mesoderm
•  ACOELOMATES:
–  No
true
body
cavity
–  Oien
soi‐bodied
organisms.
Body
Cavity:
The
Coelom
•  All
three
groups
(Coelomates,
Pseudocoelomates,
and
Acoelomates)
are
polyphyle&c.
•  Body
cavity
(coelom)
also
coincides
with
complete
diges=ve
tract
(mouth,
anus)
and
circulatory
system
(vessels
or
sinuses)
Coelomates:
Protostomes
&
Deuterostomes
Classic
division
in
Bilateria
• 
• 
• 
• 
Differences
Pahern
of
early
cell
division
To&potency
in
early
cell
development
The
forma=on
of
the
coelom
Fate
of
the
blastopore
Coelomates:
Protostomes
&
Deuterostomes
Protostomes
•  Early
cell
division
is
via
spiral
cleavage
Deuterostomes
•  Early
cell
division
is
via
radial
cleavage
Coelomates:
Protostomes
&
Deuterostomes
• 
Protostomes
Fate
of
cells
is
determined
at
early
cleavage
stages:
Determinate
cleavage
• 
Deuterostomes
Cells
at
early
cleavage
stages
remain
to&potent:
Indeterminate
cleavage
Coelomates:
Protostomes
&
Deuterostomes
Protostomes
•  Solid
mass
of
mesoderm
splits
to
form
coelom:
schizocoelous
Deuterostomes
•  Coelom
forms
from
mesodermal
outpocke=ngs
of
the
archenteron:
enterocoelous
Coelomates:
Protostomes
&
Deuterostomes
Protostomes
•  Blastopore
becomes
mouth
Deuterostomes
•  Blastopore
becomes
anus
General
Classifica=on
of
Animalia
•  Currently
considerable
debate
on
rela=onships
between
animal
phyla.
•  Remember,
Animalia
is
monophyle=c.
General
Classifica=on
of
Animalia
•  Sponges
branch
first,
form
the
Porifera
or
Parazoa.
–  Morphology
and
molecules
disagree
about
monophyly
–  Generally
considered
paraphyle=c
–  Animalia
without
true
=ssues
•  Everything
else
form
Eumetazoa
–  Animalia
with
true
=ssues
General
Classifica=on
of
Animalia
•  Radiata
are
paraphyle=c:
Cnidaria
&
Ctenophora
–  Radial
symmetry
–  Diploblas=c
•  Bilateria
are
monophyle=c
–  Bilateral
symmetry
–  Triploblas=c
General
Classifica=on
of
Animalia
•  Bilateria
divided
into
four
groups:
–  Acoela
–  Deuterostomia
•  Echinodermata
•  Chordata
–  Ecdysozoa
•  Nematoda
•  Arthropoda
–  Lophotrochozoa
• 
• 
• 
• 
• 
Platyhelminthes
Ro=fera
Ectoprocta
Brachiopoda
Mollusca