Phylum Cordata Introduction to the Fish
Protochordates
and Jawless
Fishes
Fish
• Fish origins date back 500 million years
according to the fossil record.
• There are 20,000 different species of
fish (both marine and freshwater).
• They have a very diverse array of
colors, shapes and sizes.
Cordate Characteristics
• Phylum Cordata is the most diverse
phylum in the Animal Kingdom.
• The presence of a)
– Hollow, dorsal nerve cord
– Notochord (supports the nerve cord)
– Pharyngeal gill slits
)characterize something as a chordate
Primitive Vertebrates
• The primitive cordates like the protochordates and jawless fish lack advanced structures of other vertebrates (including the fish)
• Vertebrates all have a skeleton, backbone, skull or advanced brain (protochordates do not have these)
Evolutionary Interest
Protochordates are of interest to
scientists because they are believed
to be the link between invertebrates
and vertebrates.
Tunicates
• Tunicates are often referred to as sea
squirts because they squirt water when
touched.
• Have incurrent and excurrent siphons
through which water enters and exits
• Individuals are hermaphrodites, but do
not fertilize themselves. Fertilization
and development are external since
gametes are shed into the water.
Tunicate
T
U
N
I
C
A
T
E
T
U
N
I
C
A
T
E
Lancelets
• Lives buried in the sand with its head
sticking out filtering plankton out of the
water.
• Separate sexes – fertilization and
development are external.
L
A
N
C
E
L
E
T
Lancelet
L
A
N
C
E
L
E
T
Acorn Worm
• Burrow in the sand of the intertidal and
subtidal zone where they feed on the
organic materials in the sand.
Acorn Worm
Acorn Worm Cast
Jawless Fish
• First fish
• Adults retain their notochord for support
of their body.
• Both Sea lamprey and hagfish live as
parasites and use their circular rows of
teeth to burrow into dead and dying
animals.
Lamprey Mouth
Hagfish
Hagfish Mouth