Download Chordates - sciencephs

Phylum: Chordata
All chordates have (at some point)
 A notochord
 A dorsal hollow nerve cord
 Gill slits
 Muscle blocks
 Bilateral symmetry
 Coelom
 Segmentation
 Not all of these characteristics are apparent in
adult organisms and may appear only in the
embryonic or larval stages.
Chordates: Can be with or without a
backbone
Invertebrate Chordates – Sea Squirts
(tunicates), Lancelets
Vertebrate Chordates – Birds, fishes,
mammals, amphibians, reptiles
1. Notochord
a
flexible, rodlike structure
Extends
the length of the body and is an anchor
point for muscles – allows for powerful movement
In invertebrate chordates and the jawless vertebrates
(ex. Lamprey) the notochord is present throughout
life (no backbone)
However, in the jawed vertebrates it is replaced by
the vertebral column (the backbone)
2. Dorsal Hollow Nerve Cord (DHNC)
Develops from ectoderm that rolls into a
hollow tube
The anterior end of nerve cord is enlarged
in vertebrates into a brain
The posterior end of the nerve cord is the
spinal cord.
3. Gill Slits
Gills slits are paired openings in the
pharynx/behind the mouth
The gill slits are used as a filter feeding
device in sea squirts and lancelets
Gills slits in fish develop into internal gills
Gills slits disappear in humans as they
develop
Humans – embryonic gill slits
Lancelet
4. Muscle Blocks
 Modified body segments of stacked muscle
layers
 Muscle blocks anchor to the notocord
 Fish meat = muscle blocks
 Muscle blocks develop into more developed
muscle tissue in humans and other animals
Lancelet – V shaped muscle blocks
Fish muscle blocks
5. Bilateral Symmetry:
a single plane divides body into two mirror
images
6. Body Cavity: Coelom
The coelom is a cavity entirely surrounded
by mesoderm.
A coelom provides a tube-within-a-tube
arrangement which has many advantages:
Allows visceral organs to grow independently of
the body wall
7. Segmentation
Divided into a
series of parts
8. Tail
an extension of the body past the
anal opening
 The postanal tail allows some
organisms to swim and its
efficiency has been enhanced by
the addition of fins.
 The postanal tail is present only in
vestigial form in humans (the
coccyx) although tails as a whole
are widespread among vertebrates.
Subphyla: Urochordata
 Urochordates- example: tunicates or sea
squirts
 Invertebrate chordates p. 796 Fig. 29.9
 Tunicates exhibit the dorsal hollow nerve cord,
notochord, gill slits and muscle block in the larval
(immature) stage.
 Sessile and colonize as adults—gill slits are the
only chordate characteristic maintained as an
adult.
 Filter feeds
0147.jpg
Synoicum pulmonaria a colonial sea squirt
Subphylum: Cephalochordata
Cephalochordata- example: lancelets p.
707 Fig. 29.10
Invertebrate chordates
Exhibit notochord, dhnc, muscle block and
gill slits throughout their life
filter feed
Lancelets
 small (3-7 cm long) fishlike animals that inhabit
sandy sediments of coastal waters.
 They lack a distinct head and have no cranium.
 There are 29 species, five of which occur in
North American coastal waters.
Figure 23.09a
Subphylum: Vertebrata
 Vertebrata-fish, amphibians, reptiles, birds and
mammals
 Exhibit notochord, dhnc, muscle blocks and gill slits at
some point of development.
 dorsal hollow nerve cord becomes the spinal cord
 notochord becomes the backbone (vertebral column)
 gill slits present in all embryos and maintained in fish and
some amphibians and reptiles at different stages of
development.
 muscle blocks and tail present embryonic in all
vertebrates, present in the adult form in some
vertebrates
Chordates have sophisticated equipment including . . .
a closed circulatory system with a multichambered heart
bilateral symmetry with lots of
cephalization (and sophisticated sense
organs)
an internal skeleton that grows with us
an extraordinary immune system
a digestive tract with lots of specialized
portions