/AP_Bio_Notes_31_Intro_to_Vertebr

AP
Biology
Notes
 Unit
9:
Structure
and
Function
of
Animals
 
 Introduction
to
Vertebrates
 
 A.


Chordate
Characteristics
 





All
chordates
are
bilaterally
symmetrical
deuterosomes
that
have
four
anatomical
 





structures
that
appear
at
some
point
during
the
animal’s
lifetime.
Often
these
 





structures
only
appear
during
the
embryo
stage.
 
 





1.


Notochord
 










A
longitudinal,
flexible
rod
located
between
the
gut
and
the
nerve
chord.
It
is
 










composed
of
large,
fluid‐filled
cells
encased
in
a
stiff
fibrous
tissue.
The
notochord
 










extends
through
most
of
the
length
of
the
animal
as
a
simple
skeleton.
Chordates
are
 










named
after
this
structure.
In
simple
chordates,
the
notochord
supports
the
adult.
 










In
more
complex
vertebrates,
a
jointed
skeleton
develops
and
the
notochord
exists
 










as
the
gelatinous
material
of
the
disks
between
vertebrae.
 
 





2.


Dorsal,
Hollow
Nerve
Chord
 











This
develops
from
the
neural
plate
ectoderm
that
rolls
into
a
tube
dorsal
to
the
 











notochord.
The
dorsal,
hollow
nerve
chord
forms
the
central
nervous
system.
 
 





3.


Pharyngeal
Slits
 











The
lumen
of
the
digestive
tube
of
almost
all
chordates
opens
to
the
outside
 











through
slits
located
on
the
side
of
the
pharynx.
They
have
been
modified
for
gas
 











exchange,
or
other
functions
in
chordates.
 
 





4.


Muscular
Postanal
Tail
 











Most
chordates
have
a
tail
extending
beyond
the
anus.
The
tail
contains
skeletal
and
 











muscle
elements.
 
 B.


Phylum
Chaetognatha
(Arrow
Worms)
 





There
are
60
species
of
this
arrow
shaped
hermaphrodite.
Although
the
arrow
worm
is
 





only
1‐10
cm
in
length,
it
is
the
most
abundant
predator
of
marine
plankton.
 
 C.


Phylum
Hemichordata
(Acorn
Worms)
 





Although
the
anterior
end
of
the
acorn
worm
has
a
probiscus,
the
acorn
worm
has
 





pharyngeal
gill
slits.
Water
goes
through
the
mouth,
through
the
gills
and
oxygen
is
 





removed.
The
larval
forms
of
acorn
worms
resemble
larval
form
of
echinoderms.
 
 D.


Phylum
Chordata
(Divided
into
Three
Subphyla)
 





Urochordata,
Cephalochordata,
and
Vertebrata
 
 





1.


Subphylum
Urochordata
 










The
most
common
examples
of
urochordates
are
tunicates
and
sea
squirts.
They
are
 










chordates
because
their
tadpole‐like
larvae
have
a
notochord,
a
hollow
dorsal
nerve
 










chord,
gill
slits
and
a
postanal
tail.
However,
they
only
exist
in
this
form
for
a
day
or
 










two.
The
larvae
attach
to
a
substrate
and
become
adults.
They
are
filter
feeders,
 










have
an
open
circulatory
system,
and
secrete
cellulose,
a
rarity
in
animals.
 
 





2.


Subphylum
Cephalochordata
(Lancelets)
 











These
organisms
resemble
fish.
They
have
a
prominent
notochord,
obvious
 











pharyngeal
gill
slits,
and
a
hollow
dorsal
nerve
chord.
Cephalochordates
move
like